You think it's boring? Nice argument.
Yes, I think it is the most important factor od them all and I am quite comvinced that a BB needs to be as enteraining as possible to survive in the long run. (I have more elaborated answers why it is a bad idea in global tread. No need to cross posting I think)
Usually the guy who has the chance to play at his home country asks for less money. Legionares usually cost more. As you have a salary formula in BB that is closely related to skills then tax is the only way to raise salarys for the legionares.
In RL it is often the oposite once you get to the top players in the top leagues. Out of two equally good players the american will tend to get a higher salary in the NBA than the foreigner, just like the eqaullay talented swedish player would normally earn more than the american in Sweden (not that there are to many Swedes that are good enough to compete with the random american bb player:).
Legioners tend to get higher salaries because they seek them selves to the team that pays them most. They couldn't care less if the team is domestic or foreign. It just happens that in most cases there are much more places where they will be foreigners than native. In some cases, e.g. for american bb players, the best market happens to be the domestic market. Thus the best americans tend to play there, while those that are not good enough seek there fortune in Europe (and the worst will do it in Sweden where they will become big stars).
Nobody likes to train NT members, this adds just some more twist to the game. Don't worry your swedish extreme top prospects will still be taken by top teams:)
I am not worried at all about the NT team, I actually couldn't care much less about the NT. Even if I did I would not care at all if the NT players where trained in Sweden, Pakistan, or anywhere else. There is a reason why so few vote in the NT elections (I actually do); most people simply don't care about them, so introducing a "feature" that will affact most teams negatively to possible improve the experience for those that like the NT makes little sence.