Full frame or crop sensor

I am planning on buying a new camera soon and have been looking at the Nikon D700 something that is putting me off buying it is the fact that it is full frame and if I use my current lenses with it then it only gives 5 odd megapixals. When I took a look at the full frame lenses they start off in the thousands of pounds and are out of my reach financially speaking. Due to these considerations I prefer the D300 which seems to be the top of the range but with a crop sensor. I also understand a full frame sensor will reduce the magnification capabilities of the lenses. Considering my main photography is of birds and wildlife reach is an important issue for me.
I would be interested to find out how you guys feel full frame sensors stack up against crop sensors ?
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Full frame sensors cells are larger and give better dynamic range plus better low light performance. Of course the focal lens of the lens will match the film camera so there is no more equivalent focal lengths.

Unless you are selling your images there is not any need to go full frame, even then it all depends on you subject you shoot.

Thanks for the reply GRF, I'm not selling my images, I'm still very much the amateur, but like everyone I want to be able to take the best photos possible. That has to balance against the cost of the equipment as my wife wont let me spend all our savings on lenses, lol.

freygr laid it out pretty well. Full frame means bigger pixels and bigger pixels mean better image quality. The question is, how much quality do you need? And at what cost? I shoot mostly action sports and a couple of years ago I decided to commit to the smaller sensor. I like the extra reach I get from my lenses. And I really like having a smaller, lighter kit.

It's getting a bit argumentative, but you might want to take a look at this discussion on the Canon forum about APS-C vs full frame sensors. Look past the bickering and you'll pick up a lot of information: http://forums.photographyreview.com/...ad.php?t=54205

DXOMark gives a good comparison, I think.
http://www.dxomark.com/index.php/eng/Image-Quality-Database/Compare-cameras/(appareil1)/267|0/(appareil2)/305|0/(onglet)/0/(brand)/Canon/(brand2)/Canon

I'm surprised to put my 1DSmkII and 1DkIIN against the 50D and 1DmkIII, they come out very well, the 1DmkIIN in particular scoring higher than the 1DmkIII in some areas !!

Thanks John and Paul, both interesting writeups and considering this information and my camera needs I think the D300 is the way to go for me personally.