You can get lower offset/wider rims...that would fill them out. If you go with wheel spacers, you should invest in stronger/longer wheel studs, as the stock studs aren't very strong. Look for ARP wheel studs...someone may chime in with the part number, I know they were discussed not too long ago on here.
With more area on the outside of the tire pivot point, the forces of the road on the steering and the steering on the road change.
The result can be sort of an awkward steering feel with numb spots in the feedback.
I know this firsthand, because I was running 40mm 7" wheels with a 5mm spacer as a brief experiment. I went back to no spacer and the difference in feel was noticeable. My excessive camber (2.7 degrees) also effectively improves my scrub forces because there is more tire area in the proper location that would be with a 40mm offset alone.
I notice no ill handling effects with 15mm spacers (used with 15" OEM wheels BTW) until a tire breaks traction under power, then you need to be on your toes or the car will want to dart, NOW! How my LSD plays into this, I am not sure.
If this happens at 70 or 80 MPH when you drop a tire onto the shoulder at WOT, it could get ugly quick if you weren't fully alert at the time.
I haven't noticed any degradation in feedback.
OEM scrub, which I assume to be zero, is definitely best though.
Realisticly though, the misbahavior I mentioned I don't think is any worse than when I have my 17 x 7 (42 offset IIRCC)Centerline RPMs installed without spacers, wearing shorter sidewall 205/45/17 tires.... they behave the same way. In fact they have added shortcoming of tramlining like a bitch as well.
I actually like the OEM wheel, spacers, and 205/50/15 combination better, even from a handling standpoint, than the 17" aftermarket wheel setup without spacers.
That said, my next move will probably be to 15 x 7 Centerlines, without spacers of course.