Well my D28, also the realisation of a lifetimes ambition to own one, is of 1997 vintage. I was pleased with it when I first got it, and over time it has 'played in' beautifully. However the biggest improvement to both it's intonation and playability was when last year I took it to my Luthier and got it 'Set up' He didn't do that much, checked all the grooves in the nut were the right width, and that the strings laid flat in them all the way along, he then took out the saddle and sanded it down to lower the action a bit, and he reamed out the peg holes to they sat in there more snugly. It made the guitar so much easier to play, and less painful on the fingertips too.
As for strings I struggled for a while, didn't like the Martin strings, took to D'Addarios, then tried Elixir. I loathed Elixir, found them 'slippy'. Then I tried Newtone strings, and for me they are the best I have found so far.
So persist with you D28, consider getting it set up, and try Newtone strings. They do take time to play in, most guitars do.
Giok