The electricity and water efficiency are likely terrible compared to a modern machine.

I don't doubt that, and I've considered replacing it. The lifespan of a "modern" dishwasher is about 10 years, a far cry from the 30 years that mine has run.

In the time that I've had mine, I would have had to replace a modern one about three times. I think that new ones would be more water efficient, but I do not see new ones being more efficient electrically. Mine is plumbed to hot water, so the heating elements are not used much and it dries them with blown air instead of heat.

If I am looking to reduce my electrical footprint there is much lower hanging fruit than my dishwasher. How much energy would go into the manufacturing, delivery, and installation of three dishwashers?

To your point any efficiency gained by a newer model is lost by the increased replacement cost and energy to produce a new unit every 7-10 years.

7-10 is pretty optimistic for most new stuff. Which is why I prioritize brands like Whirlpool that are repair friendly. Service manuals are readily available (often included inside the appliance!) and parts are readily available and cheap too. Brands like Bosch and Meile? Good luck - at least here in the US parts are a nightmare.

I'd be interested in seeing a comparison on this. Washing dishes is a pretty mechanically limited process. I can't imagine that much improvement has been made.

Better engineered sprayer jets, adding better sensors to determine water turbidity and other water metrics, additional sprayer arms (second-rack sprayer arms were pretty rare IME in the 90s, common today), automatic soap dispenser systems dispensing just the right amount of soap or rinse aid given on various water properties, etc.

Even today a super basic mechanical timer based washing machine probably won't work as well or as efficiently as a high end unit with various sensors and logic.

There have been improvements in the amount of water used since mine was made.

Water consumption I can imagine, but power consumption? And by how much anyway?

Improvements in these appliances always feel a little like those percentages on dishwashing liquid. If I would multiple all the improvements since 1990 I think one drop of detergent will be enough for the rest of my life.

I recon decreased energy consumption would be achieved by decreased water consumption, since less water needs heating.

I dont believe it at all.

OTOH, modern machines have difficulties to clean and dry the dishes.

Indeed, all that efficiency is lost in the hot water and time you have to spend prewashing.

That's due to environmental/green targets.