REGA VTA Question

According to REGA, they manufacture shims for those people that buy REGA tonearms for aftermarket TT's. REGA says that you should absolutely not adjust VTA for any cartridge using there own TT and tonearm. The arm tube was exactly parallel to the platter when using REGA's own Exact 2 cartridge. So, I am having difficulty understanding why REGA recommends doing nothing when the arm tube is not close to being parallel to the platter.

What would be good starting point in terms of raising the VTA? Should I start at 2mm, or go strait to 4mm? Thanks for all the input!!! It is appreciated!

The arm tube was exactly parallel to the platter when using REGA's own Exact 2 cartridge. So, I am having difficulty understanding why REGA recommends doing nothing when the arm tube is not close to being parallel to the platter.

Maybe you've answered your own question. If a non-Rega cartridge doesn't perform as well, people who don't think things through like you're doing may just go back to a Rega one, without trying to do a better setup.

Rega also recommends playing LP's without cleaning them. Unless they get a commission for each LP that has to be replaced because it was ruined, that advice makes even less sense.

Roy Gandy recommends what he recommends, for whatever reasons. You can ponder his motivations or you can seek your own answers and learn to optimize your own setup, as Viridian suggested.

Gandy stresses mechanical ridgidity over all else. They feel that Installing a shim or variable VTA adjuster nut compromises the sound and Gandy argues raising the arm up or down a few mm's actually only changes VTA angle by an inconsequential amount. Sometimes it's no bad thing to have the arm a little lower towards the back, see how it sounds to you with no spacer first. From rega's site:
Arm Height or V.T.A adjustment can be a controversial subject. Rega believes that the integrity of the arm fixing onto the arm mounting board is much more important than the questionable facility of arm adjustment: The arm should be reasonably parallel to the record surface or slightly lower at the mounting. The only time a spacer is necessary to raise the arm height is if the rear of a cartridge is hitting the record whilst playing.

I use a single 2mm. The ideal would be 3mm. Does not exist. 4 mm raises the arm at the pivot point too high. Gandy himself says is preferable to be a bit low.
VTA is not really that important except if you have many 180 or 200 grs records badly warped..
The most important improvement you can make is to get a decent constant rotational speed. You must replace the polymer sub-platter by an Isokinetic (or Groovetracer, if you are in America). Even if you have the TTPSU the Rega is not speed accurate. And the plastic subplatter attracts dust to the belt. Complement that with the Rega white Belt
Buy a standard (not the Rega Version) Michell clamp. This comes with a felt washer. Keep it in for normal records, remove it for 180 grams or over. It's the equivalent of raising the arm pillar pillar about 1 mm. Get rid of the felt mat for a further rigid coupling of the record to the platter. I found Herbie's Mat which is silicone foam a good one.
And then forget VTA. Make sure records are immaculately clean, by using a carbon fibre cleaning arm and connect the wire to the ground of your preaamp. This carries the static out which prevents dust atraction, and this way your expensive Glider stylus will last maybe one year more.. Nowadays they are hard to find. Try Analogue Seduction on eBay.co.uk.

You said:
"So, I am having difficulty understanding why REGA recommends doing nothing when the arm tube is not close to being parallel to the platter."

Fillmoor answered you question with great accuracy, above. If you want to read it in Roy Gandy's own words, go here:

http://www.n.mackie.btinternet.co.uk/documents/regaonvta.html