GS or GSPD
Both are great bikes, and either would serve you well.
I bought a 1995 GSPD, I am thoroughly delighted and would go as far to say " charmed " by the bike.
I didn't buy it as an investment, other than it being an investment in my " future happiness"
I intend to use the bike as much as possible, and take it to places that it was made to go to. Which will probably result in a scratch and a bang every now and then, if my recent trip to The Kooteneys is anything to go by.
I don't know what this may do for it's long term value, and quite honestly I don't really care. I'll be sticking with this bike for the long haul, caring for it when needed, and sharing with it some great experiences.
That is enough of a return on my investment.
Take the plunge, you will not regret it, but whatever you do, don't forget to enjoy the bike.
1995 R100 GSPD