Fact is you want an SLR for the obvious benefits, sooner or later - if you trust the gear hes selling (to have been looked after I mean, and not abused), and you can afford it of course I would buy it. Simple as.
Lugging stuff around is not to relevant as you have already stated you want an SLR, also you have accessories for your Panasonic (so you cant travel too light as it is).
Easier said than done I know - but thats my take on it, as for quotes you really need a Nikonette
to give you a realistic price there.