Originally Posted by motorinamini

I am looking into taking off the staggered rears, putting ones like the fronts back there so that all of the wheels/tires are the same, so that I can rotate them. I would like to mount the wheels with Michelin Tour HP All-seasons from tirerack.com.

So my questions are:
1) Is this a good idea? (considering I will probably get better gas mileage and that front tires cost less than rear tires)

Yes and no. IMO depends on your priority. Nothing inherently wrong with what you are suggesting but you do have to factor in the cost of buying 2 wheels. I guess factoring in the cost savings on buying smaller width tires and being able to rotate them offsets the wheel costs.

2) Will I need spacers for the back wheels if I eliminate the "stagger"? (because the off sets are different)

No not necessarily. The spacers would give it a better look but might lead to premature wheel bearing failure . However, I don't think the 15mm difference is going to make that much of a difference on the suspension geometry to require spacers.