I got DBC for my birthday a couple of years ago. Now I dearly wish I had gotten Pro.
It's not just about the lack of commands having to do with mesh deformation, sprites, or shaders, there are some serious problems I have with the language syntax features. The most notable being the lack of any way to make a global variable. I have to use workarounds like in CodeKeeper and DarkEdit, but those don't always work properly and I've resorted to writing my own little C++ app that will convert everything for me perfectly without any bugs.
I once thought limbs were a limitation. Then I saw that you could have a little bit of fun with them. The only problem is the LIMB ANGLE and LIMB DIRECTION commands are buggy, good luck with that one!
There
is an upgrade offer fomr DBC to DBPro, you save $15. Though if I were you I'd just get the super cheap download version. You can get all those models and stuff you missed out on in a DarkMatter pack or on turbosquid, and the music that comes with it really isn't that great anyway. So there's no real use for the free media they give you, if you want fill ins you can easily use primitives or make block men in trueSpace3.2 for free.
Even better though: if you know C++ just get DarkSDK. There's a whole bunch of useful organizational features in C++ that you just can't get in BASIC (mostly it's OO, but then again DBC doesn't even have ELSE IF for pete's sake).
Another reason I loathe DBC at the moment: #include. I made a post about replacing this with CodeKeeper's tapes, unfortunately CodeKeeper tapes are buggy as hell. The reason I like TAPE is because in comparison to #include you can declare variables and put other statements up (just like in C++, wowie kaboodles!).
You wouldn't be wasting your money upgrading. I have an older machine (1.3ghz Geofroce 2 MX 64mb 256mb ram) and DBP programs tend to run faster than DBC programs.

I'm going to eat you!