It depends on the patch. Those clear/whitish glueless patches are worthless IMO. Yea they will work if you get a flat and need to patch it and use it right away, but if you store it as a spare, the patch will bubble and leak if you pump it up several months later. If the tire sits for a while and the tube deflates some the patch may bubble and leak when you pump it back up. This has been my experience with the Park patch. Worthless.

I only use the black rubber patches with glue. Those are as strong as the tube itself if applied correctly and I have no problem using a patched tube as a spare or as a regular tube. Right now the front tire in my road bike has such a patch and I don't give it a second thought. I would look at the overall tube and the location of the patches (3 or 4 in the same area I would think would be a balance issue??) and make a decision from there but I would guess that maybe after 3 I would toss it. I just don't get enough flats (3 total in 1 1/2 years, and two of them were re-flats due to those glueless patches.)