There are 3 colors that are exceptionally easy to match for touchup, and those are : white, black, and silver. So I would recommend you go with the retouching idea. I have a silver frame that was fairly badly rusted, but I decided to slightly sand & respray the front end (top tube, head tube, down tube). I even put some primer on one portion that was really badly gone.
I used vaseline and paper for masking but the next time I'd use brown clay over the decals to protect them if they are in good condition. YOu want a colored clay that is easy to see, and you want to mask only the images in the decals themselves, if possible. You want something that can be removed without lifting the transfers, possibly by spraying with water. Blue masking tape lifted some of my transfers.
Note that a high-end bike like yours will have a clearcoat that has yellowed. In my case, I noticed this pretty quickly and took advantage of the lugs which were lined in black to hide the transition between the yellowed-clearcoat and the no-clearcoat new spray paint (which was "Silver Mist" GM color.) So the front is "liquid silver" and the rear is "warm silver". You can see it clearly in the final '531' picture on my website below.
http://www.ece.ubc.ca/
I did my own lug-lining, which was not as good as the original and in some cases, it took 5 tries (i.e. line the lugs, wipe it away with a sponge quickly & try again.)
With that frame the original CARLTON downtube transfers were 90% and were retouched to 100% (again, black & white make for easy retouching), and the forks transfers lost some paint due to 3M blue masking tape lifting them off.
Let the decals be your guide. If they are still pretty complete and just need minor Testors retouching, retouch them first, and if you're happy, then retouch the silver paint. You'll learn something new! If you hate it in a year you can always get it repainted, you might find a set of NOS decals for that purpose!
Replacement decals are a last resort for bikes that are in danger of not being repaintable. I've perfected my own and no matter how much time you spend, you just cannot reproduce the masterful art of the original bike perfectly. Commercial reproduction decals aren't terribly accurate and even the best painters may have trouble applying them exactly as it was done on the original bike - take very good pictures before the repaint, and give them to the painter and if possible, be in the room when he puts the decals on the bike ...
- Don Gillies
San Diego, CA, USA