If you think it is close enough, it is close enough. It does not look that bad and only you will notice it when your done. Your airplane wont complain and it will fly just fine.
However, you might be able to retrim the back edge of your cowling, change the spacing on you hinge rivets, and redrill. Fill in the old holes and you will never now they existed. This will change the spinner backplate to cowling clearance and make that gap a little wider, which is not necessarily bad. I would assume that if things shifted, your gap is not consistent between each side now anyway, so you may want to redrill that hinge to accomplish this.
Dont be afraid of the hinge pins. Some people seem to have trouble with them, but mine work well and I prefer not seeing a bunch of fastners on my cowling. That is personal preference. I think Vans got it right and hence used that method on all of their models. I can get my cowling off in minutes, despite very close 3/16" - 5/16" spinner backplate gaps (settling in nicely). It goes back on just as easily. I would use camlocks on the bottom firewall attached points if I was to do it again for other reasons, but not on the vertical sides, top, or between the upper and lower cowl. The hinges work very well. I would not switch to camlocks to fix your problem unless you where commited to using them instead of the hinge. I think redrilling the hinge would be less work.
Regardless, if you commit to fixing this, you will probably find it takes less time to fix than you have already spent worrying about it.