Know what you mean about those Astra DTI engines - much more sharp sort of rattly sound than the Pug engine used in your old Rover. Which, incidentally, was a bloody good engine.
I suppose the thing is with a lot of modern diesels, that they're not neccessarily *more* economical than the older ones, but they're much more powerful and refined (refined being a largely subjective thing), whilst still being similar in economy, with the theory I suppose being that with all that extra power they get forgiven if they're not quite as economical as the older-style diesels.
Suppose and Peugeot/Citroen pre-HDI - the 1.9TD engine (XUD I think) was a cracker (similar, if not identical in all but size to the one in your Rover) and featured in loads of 306s/406s. The 2.1TD in the 406 and XM was also pretty good - not sure what the pros + cons are of that vs the 1.9, but I think it's a fairly similar engine.
You more or less get that with a relatively low-powered turbo-diesel as well. Try a 90bhp VAG 1.9TDI - you'll be very impressed. Should be reasonably cheap in early Audi 80s, Mk3 VW Golfs/Polos, Seat Ibizas/Leons etc. I briefly had a Seat Ibiza 1.9TDI-90 and you could put your foot down in 5th gear at about 1400rpm and it's still happily accelerate from there (maybe not on a steep uphill climb, but everything has its limits). Ok, so it's got modern fandangled equipment to an extent, but not to anywhere near the extent a lot more modern stuff has, and it's got the advantage that it's been around for 15 years, and loads of people are very familiar with the engines, and they very rarely fail in any complex way.
Another one worth considering (other than a Maestro/Montego with the Perkins lump, which is absolutely fantastic) is anything with the Rover L-series diesel (basically an updated version of the Perkins engine - 16v I think). Apparently the cambelt + tensioners are a bit of a liability, but if you get them changed (or see evidence that they have been recently) then things should be fine. Basically, pretty much all the good points of the old Perkins engines in bodyshells that don't rust to pieces before your very eyes.
Heh - good plan. Is the Rangey LPG? Old V8 LPG Rangey is the way to go, I'd say.....