I think they help quite a bit. I do a lot of off-camber riding and I would never go back to a stock width machine....no way! Plus, when you power-slide corners at speed, it stays planted, doesn't want to lift the inside tire.
With my wheels and tires, I'm 4" wider on the rear axle, 3" wider on the front. I'm just a hair under 50" wide on the rear, so I can still ride the 50" trails just fine.
I would never go back to stock.....love the handling!
If your trails don't have a width restriction, I'd go 1.5" spacers. Search on ebay for Grizzly spacers, you want the solid aluminum block type with the studs.