Removing shims will reduce both the compression ratio & the compression number -- you will lose power. Restoring the lost power by adding nitro, at considerably increased increased fuelling cost, is not a smart way to do things. If you want a bit more power, leave the shims alone & add nitro until you get detonation, then back off the nitro content until it stops. As already posted, excess nitro is bad news for your engine, and without additional tuning tricks (pipe, etc), the power boost with a sport engine from extra nitro is not really very noticeable.

Live within the limitations of what you have, or buy a more powerfull engine.