It's an interesting question you've raised and I've noticed something in the replies: I don't consider everything mentioned to be a 'mod'. On the other hand, keeping with the philosophy of building the simplest RV out there, you would certainly want to avoid some of the options available stock, as well as true mods. Frankly, it'd be a fine plane with no mods or options at all; I think Van himself has amply demonstrated that. If that's your mission, be strong and avoid all temptation.
On the other hand, if you are fishing to find out the favorite mods out there with a view to what you should plan on for your aircraft, my advice would be to just look at them with a view toward how useful they are to you. For instance, I love my electric flaps and wouldn't want an RV without them but maybe you'd be happier with manual. More likely, people will disagree with me when I eschew the electric elevator trim, but I really love my manual system. I'm not really flaming Joe when I say I would never have heated seats in my RV; works for him but not for me. Favorites won't tell you what works for you.
Two mods that generate a lot of talk I haven't seen mentioned yet: Sika canopy and camlocks. I did both and I really am happy with them. I like the camlocks enough that if I bought a flying RV without them, I would rework the cowling to use them. Again, referring to the previous paragraph, others would disagree. As for the canopy, I am happy with the result and would do it again but I have seen a lot of nice non-Sikaflex installations so I am on the fence as to whether I would consider it an essential modification.
My current project is an over-the-top RV-10, so I might be a little biased toward modifications
but I think if I were building a lean -7/7A it would go like this: -7A, no options from the back of the order form except the step kit, IO-360 with dual EI, CS Hartzell prop, and Milspec camlocs. I'd stick with Van's electrical diagram (with the additions necessary for the EI), use the pre-punched panel and instruments to match, and a minimal paint scheme. This fantasy plane would probably be a gas for most of the flying I do but it's not the plane I would (or did) build for myself. Bottom line:
your behind is in the seat so you gotta decide what you do/don't have to have.