That is exactly my question too. The cars I saw did not seem to be temporary plates or its occupants were not obviously tourists or visitors. So I would imagine that it would be Lithuanians who owned these cars and I was merely questioning the source of this apparent wealth.

Talking of rich Russians, I did see a number of expensive cars (including a few fancy Cadillacs) with Russian plates at the Coronian Spit - but they usually had the suffix 39 or 91, indicating that they were from Kaliningrad (Koenigsberg)