Something is absolutely better than nothing. I did a bit of treatment and found big gains from certain small changes, but no gains from others. The key is what small change makes the most impact. For me, (small HT) filling the corner behind the FL and FR made a much better soundstage. Second best was knocking down the 1st order reflections on the sides. That realy improved the focus of vocals and killed some ringing.

Used a difuse plan for the front corners by stacking law books in a fashion to take up the corner and avoid corner loading, but also left triangle gaps between the books so there was no repetitive pattern for the waves.

Hard to explain...

Panny 3000 PJ, 118" Carada, Denon 3300, PS3, Axiom QS8, PSB 5T, B&W sub, levitating speaker wire