As a Yamaha dealer and previous owner of 2 XT600Es, Id say potentially NO !!
I paid £1700 for a MINT condition 2003 XT600E with 3000 miles on it.. YOU work it out...
30,000 miles and 14 years old, he wants to be accepting 800 quid as your going to have to be potentially doing £200 quids worth of work on it AT LEAST ! (thats unless hes already done it)..
If its well maintained and hes done the revevant servicing and maintenance (and can prove it) then yes, i'd pay £1000.
At that mileage, your looking at how well the top end has been looked after. The electrical organs of the bike are going to be wearing out (reg/rect) as are all the bearings, rear shock, linkage bushes, head bearings, wheel bearings, rotting rims as well as 30,000 miles worth of electical bodging, fetling and other adjustments...
buying an "Old nail" is always a lottery.... Even for me (Trained & qualified tenhnician and work in Motorcycle sales)
Any photos, info ???????????????
PM if you want further advice.
2001 NX650 Dominator.
BMW Dealer Technician
Ushuaia - Colombia 2007/8
UK- South Africa 2010/11
S.E Asia 2014
U.K - Magadan 2015