I have done this before, but it's not an easy call. Opening sets are usually shorter and the audience can be rude or just not that enthusiastic with an opener.
It'll probably be more like a co-headline setup, so you'll still be getting a pretty solid set from The Strokes. And, unless you're Nick Cave, the Chili Peppers are fun. I'd say do it!
It's a tough call. I've done it before, but it helped that I was taking my brother-in-law who was a huge fan of the headliner. I'd say given the bands, even if you're not that into either (and I only partially like each), they both are known for putting on great live shows.
Chilis are a strange beast. I’ve never seen them be good and yet I can see that there’s a good show in there. I think the problem is Kedis isn’t a great voice and if he’s off key on a night it isn’t enjoyable. I’ve seen them stink up a festival headline and be blown off the stage by the Mars Volta, both times around By The Way when I quite liked their stuff.