I will agree, the main features Logic Pro has over the Express is the convolution reverb, some virtual instruments, and I think better working with video as well as surround mixing- this will make it more clear:
http://en.wikipedia.org/wiki/Logic_Express
And that is just the difference between Express and Pro, it makes no mention of the other applications bundled with Logic Studio, of which Waveburner for mastering is the favorite of mine. And of course, no loops.
The point is, it would be possible to add everything the Logic Express lacks by going the third party route, but Studio is a much more economical way of adding it all. I don't see how anyone can be without convolution reverb for instance, and just buying Altiverb or something will set you back $500 anyway. But then again, Altiverb is probably better than Space Designer... so you see the dilemma.
I would recommend spending more time knowing what your needs are, and are going to be... if you want better sounding virtual instruments and that is all, then by all means stick with Logic Express and add those as you go. I'm trying out this demo, and loving it:
http://www.wallanderinstruments.com/
Great brass there.
But if you think your needs might change, then by all means get the Studio package, it rocks, and it's good for mastering and surround mixing, if you think you'll get into those areas ever. The upgrade from Express to Studio, for what it offers, really isn't a lot of money- if you even think you'll be wanting the stuff in there at some point then I'd go for it.
