buybtc.eu is not worth much because the .eu domain in my opinion. BuyBTC.com has value, and I'm not saying BuyBTC.eu has no value at all, if developed it could be a decent site, but part of the issue is in the extension...
consider that eu ie Europe speaks many different primary languages and in many BTC is not used like it is in English... for both those reasons you're struggling to pull in customers with the domain in a multi-tongued region
Most europeans know english, its taught in schools in almost every european country apart from the more eastern ones.. and there's your ticket, have a language selector to sell to all those rich europeans
I'd say the German and French markets are worth a fortune!
Thats a big generalisation on a number of levels. Not many Europeans search online in English and not that many speak English fluently... Germans and Nordic countries do but Southern Europe and France don't necessarily, nor Eastern Europe. Europeans aren't necessarily rich either... the domain isn't strong. It'd be better to have Buy(in Foreign language)Bitcoin.foreign-TLD
A website can easily make itself available in multiple languages so the language issue is not a problem. I would consider it to be a fact that around the world ".com" domains are more reputable and more commonly used then ".eu" or other domains. IMO more people will attempt to use a dot com domain before trying a dot edu.