If you're getting an iD L and have the means to get a special version I'd say go for it.
Although all three versions are very similar you do get a few extras on the special versions.
For the Princess Spacy version you get
- Same characters except Pompomtchi, Bokutchi and Shoototchi are replaced by Himespetchi, Akaspetchi and Pipospetchi.
- An extra tama pet - Kizunatchi
- Different original rooms, and the luxury rooms which cost 5000 GP are Himespetchi themed.
- Instead of the Concert Hall you get the Gotchi King's Castle but they function the same just have different songs that they play to you.
- And a few of the food items are different.
- I think the games are specifically themed too as you have Himespetchi as your sprite in one of the games.
When it comes to the happy symbols, they're different too and they can sometimes be hard to figure out as a lot of the guides assume them to be the same as the original but they're not too difficult to figure out if you know where to look and by talking to other's with the same version this gets a lot easier
For the Anniversary you get 11 new characters compared to the normal iD L but that's all I know as I don't have it myself.
I don't have an original iD L but personally I love my Princess Spacy version and was so happy that I'd gotten the special version.
I just got a P myself and I'd recommend to get both the iD L and the P eventually as they're both great versions, I don't think you'll be disappointed with getting the iD L instead of the P at first though. By getting the iD L first it will probably be easier to figure out the P if you do eventually get one as they have similar features but the P's are more complex with personality etc. added in.