new plugs (gaped proper .035 i think)
.035 is correct for a 2000.
Something I'll add to this: distributorless (meaning: 2000 and 2001 XJs with the 4.0) seem to be more sensitive to plug gap and type than earlier models. That's not to say that it isn't an issue on earlier ones, but in my experience being out by as much as 0.003 can give a noticeable difference.
Right now I've just swapped out some 10,000-mile Bosch Supers for NGK V-Powers. The Bosch plugs were good and clean, but comparing their gap with the NGKs (both of which were measured out-of-the-box but not adjusted) showed that the NGKs were just ever so slightly closer than the Bosch units. Granted, plug gaps can go out of adjustment over time, but the difference was consistent across all six plugs which leads me to believe that there are likely some manufacturing tolerances at play here. Time will tell if there's any improvement, but based on past experience I'm anticipating that the NGKs will be a better match.
I've played around with different types of plugs at various times, and have come to the conclusion that on a distributorless model with a stock or mostly-stock engine (meaning: 87-octane pump gas, no internal changes, maybe an FIPK or upgraded injectors), just use the standard OEM-recommended plugs. Even if 'better' plugs aren't causing any subsidiary issues such as poor fuel economy or running, there's no sense in spending even a few extra dollars on them if there's no noticeable gain.
All that aside, the recommendations made above are pretty much spot-on. One thing I'll add to them is fuel injectors. I recently swapped out my decade-old OEM units for
0280155917 injectors, and have seen about a 1mpg improvement across the board; YMMV. There are other maintenance considerations I need to take care of (tranny flush being one of them; it's overdue) that could possibly result in further improvements, but given that probably 90% of my driving these days is around town, getting 14.5mpg vs. 13.5mpg is a definite improvement.