Same reason you are afraid to remove it.

Because it's easier to cover up than remove. :-) They did the same thing on the 1920 house we're rehabbing.

We took the aluminum siding off of our last house which was a 1926 bungalow. We did it one side per year, restoring what was underneath by ourselves. We had shingle on top, clapboard on the bottom. The shingles were pretty dried out and some of the clapboard was split and had to be replaced, but really it was very salvageable. After we did ours, the neighbors across the street did theirs, which was all shingle, no clapboard (I was jealous). On theirs, the company that installed the siding hacked up some of their window trim so they had some repairs to make but again, is was very salvageable. Now in our current house, our neighbors two doors down removed their siding and restored.

We bought a set of scaffolding which made the restoration job much easier. If you're interested in going that route, look on craigslist. We just sold ours there and there were other sets available too.

Be prepared for repair. Perhaps wait until it's in the budget. We had faux brick on our old house and knew there was clapboard below (one of the squares of the brick stuff fell off everytime there was a stiff wind). When we removed the faux brick, we found a big fat mess-windows had been replaced but the claps weren't, it was just filled in, blown in insulation had been done via MANY 4" holes drilled into it, pieces were cracked, etc. We eventually decided to just remove it because of other propblems so we could get to the sheathing underneath and do repairs, then replaced it with vinyl (I know, I know-but the house was pretty hacked anyway, and we did wide corners and trim in a different color than the body, so it echos the original look).

+1

I would examine a small location and prepare the budget accordingly.

Do it right once and be done with it though.

Budget wise FWIW we just did a complete tear off, Tyvec wrap, and resided with LPSmartside vertical siding on a 2K sqf ranch. It was a little under 12K, and we did not do any of the work ourselves. Vynil was quoted to us a 8K and fiber cement 15K.