I get your points about suspension and tyres. The tyres are an easy part, but suspension can be an expensive excersize. I guess I find the stock set up of the DRZ pretty good for what I do, which is mostly single trail. If anything the front end is a little soft in the mid stroke and slow on the rebound.
The main reason for going to an FMF system, was for a bit of bling or love for the bike, and I have always been worried about the header getting crushed. I recon the stock pipe takes away from the look of the bike too. The FMF header is stronger (being stainless) and adds a bit of grunt (so I have heard). I am hoping it gives it a better exhaust note, as I am not to fussed on the noise the stock system makes.
Losing weight in the case of the DRZ is always a good thing, and seeing as I am putting a rack on it and a few other odds and sods I should end up about the same or a little lighter.
Thats what I love about the DRZ though, most differ due to how we accessorise them.
Ride safe
Goodie