billd91
Not your screen monkey (he/him) 🇺🇦🇵🇸🏳️⚧️
Nope, you just summon crazy creatures with no metamagic style adjustment in spell level. I believe the feat was at one point intended to be as you say, but it certainly wasn't written that way, or errata'd later to be that way. Thus, you can toss out a greenbound wolf at first level, and have it throw out a wall of thorns, because the world is occasionally ridiculous. Aberration wild shape might actually be even more ridiculous, at least at the level you get it. It's hard to beat combining nilshai form from unapproachable east with enhance wild shape from the spell compendium, granting two spells every round. It's not like that's the only crazy form either.
I doubt it was ever intended to raise the level of the summoning spell. But one thing to keep in mind is that any greenbound creature summoned by the summon nature's ally spell is generally going to attack as best it can. That's what summoned creatures do. You need to be able to communicate with it in order for it to do anything more sophisticated, like use the wall of thorns spell-like ability. For most druid characters, that wouldn't be too hard, but it's not something nature's allies just do because it's tactically best to do right now - they need to be directed in a way they understand.