Anything the VIIC/41 or 42 subs have better?

[Incubus]

I've never actually gotten these. Before GWX, I had a career that lasted all the way to '44 with a type VIIC- pimped out electronics, U-flak, the whole nine yards. I gave up because I just wasn't skilled enough to survive all those little British terrors combing the North Sea/atlantic (it got to the point, somewhat realistically, where I'd get a safe opportunity to sink ONE ship, spot maybe 3 but be too dangerous to engage (there was like a canopy of aircraft, I swear) and have to head home bringing in ~5,000 tons a patrol.

I have GWX, and I know that means more challenges. However, I am kind of curious if it is worth getting the /41 or /42 subs. The problem is that if you buy a new sub, you have to re-buy ALL the upgrades for it, which costs a ton of renown. It forces you to make a hard decision- keep a rapidly outdated model stock to save for a better one, or upgrade your sub as you go along?