Replacing Shower and Tub Valve Set - Questions

I am considering replacing back-to-back shower/tub valves (Moen Dialcet) originally installed in 1965. The valve is dripping on one and the diverter drips to the tub spout on the other.

Questions:
1. How much improvement will I get with a new valve? The heads have been replaced and are satisfactory.
2. One valve is above the other and I may have to replace about 4 tiles (4") for good access. Is it possible to reverse the hot and cold inputs on one of the valves so I don't have to do some kind of "crossover" piping of the supplies?
3. Are there any acceptable alternatives to soldered copper piping connections. I plan to use the supply, shower head, and tub pipes already in the wall.
4. Is there much difference if I use a pressure balanced valve versus a thermostatic controlled valve.
5. Any recommendations on brand and model of the valve?
6. The current valves have the diverter in the valve but most that I have seen have the diverter in the spout. Is that a characteristic of the brands? The bath spout is rarely used and the diverter in the valve is convenient, but it is another possible point of failure in the valve.

Thanks for any suggestions.

1. Maybe none, since flow control is in the shower head, not the valve
2. It depends on the valve. Most, but not all, single handle valves can be reversed for back to back plumbing. You have to read the instructions to see if it can be done, and how to do it.
3. Not to a plumber.
4. It is a personal preference.
5. That is also a personal preference, based on what you like.
6. Few manufacturers make a built in diverter any longer. And few companies stock them even when they are available.

You can get a Symmons Temptrol with on board diverter.

If you install the pressure balanced valve properly and according to instructions and there is a large variance between the summer and winter cold water inlet temperature, you need to readjust the limiter in the valve each season change. This is inside the valve, or at least behind the handle. Most people don't do it, and this either leads to too hot in the summer, or too cool in the winter. Most (not all) pressure balanced valves are single handle and you have no flow control...it's either full on, or full off. And, as you use up the hot water, you adjust the valve to retain the same temperature and put the valve in a different position winter/summer to find your 'perfect' water temperature. Most (again, not all) thermostatically controlled valves have a volume control and a temperature control. So, you set your desired temperature, then adjust the volume...it stays pretty much the same season to season. I prefer a thermostatically controlled valve, but they do cost more, and are more expensive to repair when the time comes.

The Delta 1700 series rough-in valve will let you chose three different 'guts', so you get a choice (at different price points), so it is quite flexible, and you can change your mind down the road by changing the trim and cartridge.