Here's my 2 cents:
For valve shimming I'm not sure what kind of accuracy you are looking for. You can easily get +/-.001" accuracy with a cheap digital caliper if you practice. That would be my advice. In digital calipers, there are good models and chinese models, and in my opinion, nothing in-between. Fowler sells chinese calipers at an attractive mid-market price, but these are really low priced calipers marked up. Chinese calipers are typically stainless steel and the faces may or may not be ground properly. If you are going to buy Chicom calipers, buy them at HF where they can be had cheapest. Know that they can be improved by careful disassembly and cleaning.
Mitutoyo really owns the digital caliper market place. They are smooth, easy to read, and offer excellent battery life. The working surfaces are carbide and precision ground. They are really the gold standard of digital calipers. I also have Starrett 798-8 caliper. Past china made models have been troublesome and Starrett lost some if its good reputation over them. The 798 are USA made using Swiss electronics (similar to Etalon, Tesa, B&S etc). My set is coolant proof which may be helpful for automotive work.
For mics, I have digital Mits and old Starrett 436 (bottom of their range). I find myself reaching for the oldies most often. If you are looking for a decent mic, here are the features I think you should compare:
1) Grip- I like the smooth rounded frame on the 436 as opposed to the new rectangular grips. If you need to work below .001" (.03mm) you may need an insulated grip to prevent your body heat from affecting the reading. A mic stand is another solution and I recommend it. Lufkin made similar grips/frames. You can poke around on ebay to find comparables. My B&S from the 70's 80's had the new style rectangular frame I personally don't care for.
2) Friction or ratchet clutch? Many prefer friction clutches for finer work. But you really have to practice your technique with either using a known std. I think most Starrett 436s are ratchet.
3) Markings- I prefer Starretts' markings. I think they are easier to read. Starrett put a lot of thought and work into making hash lines clear and readable. In my opinion, they are the best in the industry at this. My 436s have lovely easy to read markings.
4) New or used? Some of the recommended mice are very expensive new. The Starrett 436 has been around for ever. You can pick them up on ebay for less than $20. If you want new, the polish made models sold by Enco are said to be very good. Japanese made fowlers are also good. Avoid chinese made (not because I don't like China, but because they make poor quality calipers and micrometers - exception: ANYI very good stuff).
My recommendation- digital caliper. If you can afford it, buy Mitutoyo. If you can't, HF will work.
For mics, I recommend a used Starrett 436M. Metric is not as common as inch sizes so it will cost more. You might find better deals on Mitutoyos. For new, buy the Enco made in Poland models.
