I cannot speak to tire width but it appears that the maximum tire height (e.g. diameter) you can run without a lift, regardless of rim size, is just under 30". There is a tire section over at
viewforum.php?f=124 that you might want to check out. There used to be a chart for the fit of various options but I cannot at the moment find it.
Personally I'd spend my money on more critical things than new rims. Just clean and polish the ones you have and spend the $s you save on a timing belt (must be done at 100K miles or earlier for a vehicle that's now 7-8 years old), Samco CAC hoses, and a GDE tune.