Riggle VTAF question

Hi, all.
I have a question which I hope will prompt plenty of opinions and help. I listen to albums via a Rega P-25 and Jolida phono preamp. I added the Pete Riggle VTAF successfully a couple of years ago (or maybe just last year). It raises the tonearm as you may know. Well, I just cannot seem to make myself use the shims for the cartridge that Pete suggests, so basically, I can't really adjust for VTA since when the adjuster wheel is rotated until it can't rotate anymore (to the top), at that point only my 180 gram vinyl plays with the arm level. Otherwise I am always slightly higher at the rear of the arm since I haven't put on the shims for the cart. The reason I don't want to use the shims is I'm now using expensive (to me) carts (Shelter 501 and the Denon 103R -cheaper but to my ears sounds better than the shelter for some reason) and I don't want to mess them up. Bottom line questions:
1. What are your thoughts on using or not using the shims? 2. Is there a way to raise the platter with a mat or something that could solve my dilemma? I had been using the Iron Horse acrylic platter (same height as glass), but just switched back to the glass right after I installed the denon cart.
3. Has anyone else out there had this problem (er. . . dilemma)? If so, what have you done?
4. Not totally off topic, but while I'm posting, any reason why the denon might be sounding better than the acclaimed shelter? (I know - the denon is acclaimed too) The styli sure sit differently. And, if it matters, I use the Baerwald alignment by using the Geodisk (not rega). Thanks in advance for any comments about any of this.