The only issue I see with that is as the number of projects increases, the total focus decreases. The more projects you have on your plate, the more switching you have to do. So you may lose time getting back into gear and focusing.
On the other hand, insights from one project might help out another.
That's my point. The most that you can give to any combination of projects is 100% total. If you have two projects, one of them will have to suffer, or you will be forced to give them both 50% focus.
I'm saying something different though. If you have 2 projects, you won't be able to split your time as effectively so you may have 40% focus for each, and so on. As you take on more and more projects, the time it takes to get back into the groove increases. You are likely to spend a lot of time moving between projects and this will disrupt your overall focus.
Ahhh now I see what you're saying. You make an excellent point.