FYI - you can find re-pop 341s for right at $1000. I've bought and sold about 10 CB750s over the last 5-6 years and if they don't have original pipes I usually buy used ones (if I can find them) or now, that you can get re-pops again, I buy those. Typically, when somebody shows up to take a look, the pipes sell the bike. I usually don't have a bunch of cash in the bike to start - I try to find complete original bikes, but they just aren't out there like they used to be. I do all the mechanical work and painting so my labor is "free". That is the only way I make money on them. If I had to pay myself for labor, I'd break even at best.
I agree that clean, original and complete bikes bring the money. But, I usually get between $5-6 for mine when they are done. Mine typically don't go to investment collectors. They go to the guys that used to have one or just want a good clean, nice vintage ride. That's my niche. So, in my case, I do get a little return on my investment. Just not much. The thing that I find that sells these bikes the most is re-plated fasteners, shiney paint and shiney pipes. Everybody sees the paint first, but there is nothing like 4 gleaming chrome pipes.
Restorations, if correct always seem to sell easily and for good money. I don't like spending $8000 to make $1000. That's why I've kinda settled into my $5-6k range. More people can afford them and the investment collectors really are looking for the early ones and very low mileage originals.