In the South East (the region I live in) it is very likely that of the 10 seats there will be at least 4 Tories, 2 Lib Dems, 1 Labour, 1 Green and 1 UKIP. It could boil down to a race between the 5th Tory, 2nd UKIP and BNP.
In London the Lib Dems were a handful of votes away from a second MEP last time, with no chance at all of the Greens getting a second. In the South-West again a second Lib Dem was much more likely than a Green. In the North West last time it was a second Lib Dem who got the last seat, just pipping the BNP.
So basically swinging 3 per cent of the vote *does* make a considerable amount of odds, and it does matter who that vote swings to. In the four regions above, at least, there is little or no point voting Green 'to keep the BNP out'.
Dunno about the south-west, but in the north-west (and yorkshire where a very similar tale could be told) you are wrong. Tne BNP are ni the stronger position, and the greens playng catch up - both with them and he lib-dems - but they were not far behind, and it is perfectly plausible that they will make up the necessary ground. there's no Respect this time, which might only be worth 1% or so, but that aint to be sniffed at.