No it isn't a silly questions - yes the 7D has the better AF system and the dual processor (giving it the faster frame rate), but the 550D is still a very good camera. I've not done a side by side comparisson (I assume from your statement that you have) but I see no reason why the 550D won't delivery very similar image quality, it will just need more care to get the shot. As for whether the extra cost is justified I think that's not an easy one to answer. If you already have a decent lens and can afford the 7D then why not, but if you're looking to start out and on a limited budget then a 550D with a better lens will outperform a 7D with an inferior lens.
I feel that there is a tendancy to dismiss the entry level bodies to quickly. Sure they are a bit slower and smaller (which suits some) than the 50D/7D ranges buy they are also a hell of a lot cheaper too and as such are a great starting point (I guess that's why they are often referred to as entry level)! For the first three years that I shot with Canon I used entry bodies (350D and then 400D). I have since moved on to 'better', more expensive bodies, but still some of my best shots were taken with the 350D & 400D.
So is the extra cost of the 7D over the 550D justified? Only the individual who going to spend their own money on it can decided that one. Is the 7D a better camera than the 550D? Yes, but then from what I've read the 7D is a toy compared to the mkIV...
Good call Peter! I've just picked up a 400D as a down grade from the 50D for my macro work and couldn't be happier. The smaller size suits and the mp, FPS, AF etc. aren't an issue. For £150 I'm well happy. Saves the 50D's shutter for other things
