Mark,
To be honest with you, I would take the wheel spacer money and apply it towards a set of 18" wheels first. 17's do not do the car justice at all and would not fill your wheels well so the spacers are useless. You would also need bigger spacers since the 17's have a smaller offset. Go for a bigger, wider wheel and then see if you need spacers. I did 18x10 in the rear and 18x8.5 in the front.
If you did put spacers on a 17" wheel you would need bigger spacers to compensate for the offset. I think that going over 5mm will affect the weight distribution and have a negative impact on the wheel bearings over time. Get new wheels first!
