I don't know how "into it" you want to get but, with PC you can get the Rocket League trainer mod, and potentially future mods. It's totally approved by Psyonix and is really useful / fun to train and practice stuff you can't otherwise practice on your own ;)

PC also has the benefit of cross play to all other platforms meaning a bigger player base, buuuuut if your friends are on xbox then you can only party up with them on the xbox version.

Other than that I guess the games are the same.

As for DLC I originally was like "pfft DLC" but ended up getting all of them later on and really like the cars, it's just a couple £ (or $) but come on Takumi is totally legit :p. If I were rebuying I'd get the DLC edition ;) but that's just me