I just bought a 1970 Triumph Bonneville the other day. Its probably 95% stock and should be pretty easy to restore.
Best of all it runs and rides really well. I grew up around Brit bikes as its what my dad competed on for years. In fact, I still have my dads 1956 TR-6 Triumph Hill climber that he competed on professionally.
The 1970 was what most folks consider to be the last good year of the Bonneville. Its when they were at their peak before the BSA corporate managers took over the operation and screwed up lots of things.
They put government mandated blinkers on them, different headlight mounts, etc...
Oil flow was said to be not as good with the oil in frame models also.
There are a couple of forums to check out for more info on these bikes
www.britbike.com is one of them that is pretty good.
Look on e-bay also as there are lots of different years of Triumphs on there as well as parts for sale. It will give you a good idea of what people are willing to pay for them.
Anyway, let me know what you end up deciding and if you have more questions. I have several Bonneville books with good info in them regarding restoration and desirability of different years.