Well I am STILL in Estonia, it is almost 4 months now and I will stay a few months more.
My "theory" was not wrong but it needs some adjustments as I identified several types of girls and certain tendencies to be accounted for:
Type of girls:
Russian: These girls expect guys to pay them everything (drinks, going out, etc) they are not picky and will sometimes do what you want in order to get free drinks. I met quite a few like this. Once they realize you're not paying more drinks to them, they'll make up a way to get rid of you. Usually they go out in groups of 2, 3 or 4 girls and can be extremely beautiful.
Russian/Estonian mix: These girls have the strong personality of the russian ladies and the relaxed no-worries attitude of an estonian. Their mood variates all the time between being cold and not giving a crap and being really gentle and making you feel like a prince. Generally they're looking for guys with money to travel for free, get gifts, etc.
Estonian over 25 years old: Due to the influence of Russian regime these girls are a bit more closed usually, tend to answer with inconclusive responses like "maybe" instead of "yes" or "no" and sometimes it can be hard to get to know them since they're reluctant to speak about themselves unless you ask specific questions.
Estonian below 25 years old: With little of no influence from Russian regime these girls are quite relaxed, talkative, friendly, funny and appreciate relaxed guys with a good sense of humor.
Generally Estonians: Girls expect guys to pay most things when they go out but some might pay their own. The thing is that these girls tend to imagine that because you are a foreigner you are somehow rich. Or at least they consider you rich compared to them so they want you to pay for everything.
As for my experience, I have met quite a lot of ladies but I am extremely picky with whom I actually spend my time with. I can say in 4 months I only met one single amazing girl, the rest I didn't find interesting but were OK for socializing a bit and some casual fun.
If you're looking for casual fun, you have about... well... 100% chance of getting it, even if you are fat and ugly, every night, at no cost or just with one or two drinks, if you know where to go.
I have observed for quite some time the interactions by staying full nights in a disco watching people come in alone and hooking up with someone, usually after some drinks but sometimes even without drinks. I've watched how they do it, how to spot the girls who are available, those who will go with just anyone, those who will go only with nicer guys, those who will need convincing and those who are completely not interested in meeting someone and are just going with their girlfriends to watch the live band and dance.
Yesterday specially there were a lot of lesbians in the place and I had quite some laughs watching guys hit on lesbians without realizing they were lesbians... then suddenly the girls just start kissing and the guy slides away realizing he ain't getting any action! LOL it was hillarious.
In this disco at around 2-3am most girls are already hooked up with some drunk foreign guy and the ones who aren't get "attacked" by multiple guys one by one in intervals of seconds so they won't even look at you if you try to talk to them, they'll just nod their heads and completely ignore you.
I once took a girl to see the live band, I left her sitting on her own for 3 minutes while I went to WC, when I came back there were 2 guys one sitting in front of her one sitting next to her while she pretended to find something in her purse to avoid the guys. Was quite funny because she is not used to it and was kinda scary for her. I did warn her once I get up it will only take seconds for guys to start hitting on her... and she told me right after I got up ... so it was. hehe
From 22:00 you have live music but the entrance is paid usually 7 euros. If you go around 20:30 it is free entrance so you can enjoy some drinks and meet some girls. This place is usually half-full or full almost every day of the week and it is like a jazz club not a disco or bar. Here you can meet foreign ladies, russian ladies and estonian ladies.
Russian ladies usually go to get free drinks, in exchange they let guys hold them and if they really like you or are more slutty they even let guys take advantage a bit. They might invite you to go to a disco with them (you have to pay all the entrances and drinks so expect to spend quite some money), they drink usually wine bottles starting at 23 euros and enough for 4 glasses of wine.
Foreign ladies are very approachable and they might even pay YOU drinks so it is also cool if you're into older women who don't look attractive like russian or estonian.
Estonian ladies are not so approachable but some might be there to get free drinks, they are more picky usually but not always. I have seen young 18-19 year old girls getting drinks from guys with 50-65, it was so damn weird to watch that!!
Amigo (disco in Viru Hotel)
Best hunting ground, you can find foreign ladies and russian/estonian ladies looking for foreign guys to make out and have fun or even one night stands. Mostly estonian ladies which is better than russian. The girls are usually half-drunk and guys take advantage of that. I have seen crazy things in this place like 4 guys making out with one girl, at the same time. I find it a bit discusting but oh well, if you are into this kind of girls go for it! :p
You might want to go in early to meet girls before they are too drunk. Last time I went I got pulled to a table with 3 ladies, who were drinking champagne and got myself a free glass of champagne. The cutest lady was with her boyfriend and asked me my number for us to meet up and go out... but honestly I wasn't interested so I didn't give her my number. The boyfriend was a bit jealous but the thing is that these girls do this all the time so the guys have to put up with it in order to keep the lady. Estonian girls will do what they want, most of the time, you can't really control them. It is very common that women who are married or have boyfriend to end up in some disco kissing other guys. Decent girls normally don't go to discos.
Vapiano (usually good for lunch or dinner)
Good place to meet ladies, nobody is drunk so you can actually MEET someone for real. Girls rarely go alone so pay attention as they might be expecting company. They do go a lot in groups of 2-5 girls so you can try sitting up near 2 girls and start casual conversation or even let them do the talking.
The staff is quite friendly, I got to know most of them by now.
There are a few more cool places too but enough for now.