Ted, I live east of the Continental Divide, but my wife and I both grew up on the west coast and we have a lot of family out there. The Aztec is a solid, reasonably well equipped IFR platform, but is naturally aspirated and the one shortfall that has me thinking of upgrading is single engine service ceiling over the rocks. Going west I always fly it light and pick my days and routing so I always have an out well above minimums. But I am now considering stepping up to a turbocharged twin. Pressurized would be nice, and the Finance Minister would prefer it when she is a passenger with me, but I am wary of the added cost of maintaining the pressure hull.
I note that you've been happy staying with unpressurized twins. I am probably going to shortly fire up the spreadsheet again to do some analysis in preparation for a possible decision later this year, and appreciate any advice and the future opportunity to ask questions.
A good part of the reason why I've been happy with naturally aspirated piston twins is because about 99% of my flying is east of Denver. I've have managed to successfully make trips across the Rockies, even in the heat of summer or in the midst of some rather odd winter weather. I've also said that if I was going to make regular trips in that part of the country, especially on a schedule, I'd be looking for turbos and likely pressurization.
Keep in mind that turbos give you improved altitude and single engine performance, pressurization gives you comfort and some extra safety due to lower hypoxia concerns. You can fly at altitudes you normally fly a pressurized aircraft on O2, but nobody likes it.
Turbos increase cost in the form of higher engine overhaul costs, higher fuel burn, and then there are more items to break and that do break. From a practical perspective, the increased fuel burn is typically most of what you'll notice, and it's not necessarily that bad if you run LOP and pick your altitudes properly. You'll probably need to replace exhaust components if you own the plane long enough, and those can get spendy. A T310R is expected to be in the range of $450/hr "all-in".
Pressurization increases costs further. Most of it comes down to leaks in the pressure vessel that need to be repaired somehow. Door seals become important to maintaining maximum pressurization differential. Windows become structural items. Windshields are spendy (~$25k each), but they don't cost anything until they break. Most likely you'll be chasing things like door seals, pressurization tubes into the pressure vessel, etc. Plus anytime you do something that goes through the pressure vessel requires a DER since it's a structural item.
A 340 is typically considered a ~$550/hr "all-in" plane (insurance, MX, hangar, fuel, etc.) if flown around 100 hours per year, and will get you 190-220 kts depending on how you fly it and the specific plane you have. Most people I talk to seem to do 200-205 in the low flight levels. Useful loads on the 340 can be a bit low, which drive some people to 414s or 421s. Those also have more space but take more runway and cost more to operate, plus require larger hangars.
Of course, as with any plane, it depends on how you own it and fly it. Most 340 pilots are ROP fliers, but the LOP ones see a significant fuel savings. Some put $100k panels in, and some are happy with steam gauges. There's a wide variety out there.
So, here's my plan. You buy a 340, and sell MotoFlier your Aztec. Done.