My advice given the lack of knowledge regarding the history is to change valves more or less immediately - they are after all so much cheaper than an engine rebuild.
I have a photo used to scare "youngsters" that shows what happens when an exhaust valve drops - and an OEM R65 is good for a valve drop any time after 50,000km (and yes that will buy me an argument in some quarters, but at one stage I had a collection of ruined R65 engines that had all dropped valves and they all had around that mileage).
Intervalve, sold by Motobins, are a good alternative to OEM (I use them, but then as my valves are somewhat larger than stock there is no OEM path for me). Lead free seats are available and a bit cheaper than BMW, but if you have stock sized valves, OEM is probably best - it took BMW a couple of goes to get it right, but in the end they did.
That said, if your seats are still serviceable I'd be inclined to "suck it and see" as replacing seats is not trivial and you may not need to - just monitor tappet clearances and if they do not sudden;y start closing up - golden.
The big thing is to use a quality machine shop that knows what they are doing! Butchers have ruined countless BMW heads. There is nothing difficult about working on them, but there is a skill-set needed. Any shop that works on VW air-cooled heads will have all the necessary skills/experience.
If your valve guides have not shifted I would be inclined to not replace them - have them K-lined which gives you pretty much the same life as a new guide, and when the insert wears out, the machine shop can replace the insert in minutes. Using a K-line does reduce the contact area of the stem in contact with the guide and some have argued that this effects heat transfer. They are correct, it does, and the difference is about the same as the difference in a rider's speed over a good hill, with and without a pre-ride bladder emptying.
Whilst getting the new valves have your rockers refaced. BMW were notoriously parsimonious with the depth of their hardening treatment so after your rockers have been refaced, take them to a black smith and have the contact areas properly hardened (preferably an old Blacksmith who still has, and knows how to use hardening treatments containing cyanide like "Hardite").
If in the process of refacing the rockers the existing needle roller bearing shells are destroyed (ask me) don't despair, they are catalogue bearings (bless you bmw) and you will need to make up a mandrel, shaft and sleeve to press out the old ones and press the new ones in. When pressing in the new bearings - all the rollers should be present (ask me how many bearings it took to learn this) to spread the load and avoid caving in the end of a brand
new shell.
BTW, the first sign that you have picked a good machine shop is that they fit the keepers to the valves and ensure that the valve is free to rotate inside them and that the retaining ridges int he valves match the keepers perfectly. My original keepers were rejected by my shop, but the cool thing is that in the arcane world of engine rebuilders keepers can be sourced from sources other than BMW and therefore cost cents rather than dollars.
A final comment on the topic off seats. If you do decide to have new seats put in and if you decide to avoid the cost of BMW lead free seats, you may be offered the choice of press-in or screw-in seats. Contrary to popular mythology, screw-in seats have no better in-service record of failure than pressed in seats - providing the machinist knows what they are doing. I watched the seats get put into my R100 heads recently - the machinist spent a long time on the mill setting up the desired level of interference and when the heads came out of the oven he pressed the seats in with a little 12 ton press. He does thousands of VW head each year and can count seat failures in the last few decades on the fingers of one hand.
