Wheel question

[CleanNeon98]

Here is my car and the current setup

2004 Mazdaspeed
FM Springs (soon to be H&R Race)
FM Sways set on "neutral" settings (soft front, mid rear)
16x7 +35 BBS RK
205 50 16 Eagle F1 GS-D3 tires

And just for fun...
FM complete intake
FM Downpipe

I don't really have a problem with my wheels aside from them being black but that's not really important here. I am looking for something different. I wanted to go with a 16x8 +15/20 but can't seem to find decent ones anywhere.

I am trying to sell my wheel and tire package for 1000 obo, so far the best offer was 800 cash but I can't really get much for 800, nothing that would be comprable to BBS wheels and GS-D3 tires.

I am wondering if there are any benefits of going to a 15 inch wheel. It might look goofy, but what benefits are there? I would expect more sidewall flex due to taller tires, but a little more acceleration.

I am overall confused on all of this and just deciding if selling my current setup is worth it to replace it with cheap wheels and tires.

Please school me on this.

Things I've found so far within reason but still all over 800
6UL 15x8/9 with 225 45 ventus rs2 (on either size)
RPF1 16x8 with 225 45 ventus rs2
Rota slip 16x8 +20 (concave center) with 225 45 ventus rs2

Not really a fan of Rota wheels so thats not on the top of my list. Basically trying to figure out if it's worth it to go wider, I talked to Keith and he said if I wanted to I could run a 225 45 on my current 16x7 but I imagine with sitting so beefy, response would go out of the window.