Ian,
It sounds as if the PO was sold the wrong springs or he rode solo and was much lighter then you. Springs are rated by spring-rate, the amount of force needed to compress the spring XX distance. The springs should be selected to match your weight. And if you have a pillion passenger frequently - the combined weight of both of you and anything you carry on the bike (like clothing, camping gear, etc.)
Lowering a bike by lowering the spring rate is the WRONG way to do it. Ideally - you want to limit the maximum extension of the shock, while maintaining the minimum compressed length. Your mechanic may be a fine fellow - but BMW sells a lowered R1200R that does exactly that. IMHO, he's not being entirely clear. If what he meant was he wouldn't lower a bike by putting softer springs on it - then he's 100% correct.
Using a shorter fully extended shock means the bike is lower when the suspension is uncompressed, but the same distance from the ground when it is fully compressed. This results in less suspension travel - which generally means a higher spring rate spring is needed to prevent the shocks from hitting the fully compressed length in normal use. It also means that nothing will touch down any sooner than with the stock length suspension.
I'm on the fence about progressive springs. I have a full Hyperpro suspension that was built to my rather exact spec's - and then modified to make it even a better match to my riding style. That was possible because I'm a good friend of the US importer of Hyperpro, and he was willing to spend some time with me, and toss ideas around as to how to do this. I originally had the progressive springs on front and rear - and ended up with a progressive front spring, and a linear rear spring. I simply couldn't seem to get the preload correct with the rear progressive.
The first linear spring I tried was too soft, and the suspension felt harsh because of that (due to it bottoming out.) I went up one step in spring rate and things improved. I also very carefully adjusted the dynamic sag (the amount the suspension settles with my weight on the bike) to about 1/3rd the travel of the suspension. That made a BIG difference.
Just throwing softer springs at BMW's marginal shocks in the hopes of lowering a bike is really the wrong way to go about lowering a bike - and whoever sold you those did you a disservice IMHO. Dunno who the Oz distributor of Hyperpro is, but if you bought the springs through a dealer, it might be worth talking directly to them about what you want to achieve and how you use the bike. Correctly lowered - you can get a comfortable ride and your tootsies can reach the ground.
I do not suggest trying to lower an R12R any more than about 3/4" (which is what BMW lowers it.) Every fraction of an inch you lower it comes directly out of the suspension travel (on a normal lowered suspension - mine is a bit different, but we'll leave that for another day), and that means you're more likely to bottom out the suspension, making it much less comfortable. Note that 3/4" at the wheel is NOT 3/4" at the shock, there is a lever multiplication factor between wheel travel and shock travel (or stroke..) and it's different on the front and rear. Luckily, it's easy to calculate with a simple tape measure.
BMW greatly overstates the actual travel of their suspension, by at least 20%. The travel they quote would only be true if the rubber bumper on the shock wasn't there or magically became infinitely thin when the shock neared full compression. Problem is - the bumper IS there and for it to protect the shock - it can't become infinitely thin. This means you have less travel to play with (by lowering it and reducing the travel.)
I had the opportunity to ride a friends R12R that had Wilbers shocks on it that lowered it 2". It was simply awful and IMHO unsafe to ride. We swapped bikes - and he couldn't believe the difference. He ended up getting a normal height Hyperpro suspension since he didn't need the lower suspension (the bike was used and had come with it) and he was then a very happy camper.
For more on setting up suspension, I've condensed a number of long posts I made here some years ago - on my website. You can find it here:
http://www.eilenberger.net/Suspension/suspension.htm
If you have any questions on suspension, I'll try to help as best I can. I'm not a professional, but I have spent a lot of time on multiple bikes figuring out what works, and what doesn't. The first lesson I learned was using a softer spring to lower a bike is not going to be satisfactory. I've been quite happy with my current suspension for about 60,000 miles now, and see no reason to change anything on it. It's lower and comfortable, and really gives a great controlled ride.
Best,
