If you're talking about upgrading a late '40s Herse, I object. But for a common bicycle such as the Sports, I don't think it's that big a deal. When I take on such projects, I strive to make changes than can be undone if necessary.
Switching to aluminium rims will save a tonne of weight. It will make the most noticeable difference.
FYI, I built 700c wheels for a ladies Raleigh Sports and could run tyres as large as 700x32 and still clear the mudguards.