I don't have any opinions, but i'll be happy to share some facts

The camera you have is very desirable. It is both a fine camera, but fairly uncommon.
It is a first rate camera, mechanically sound and not just 'an economy model'.

That's a 2 sentence condensation of a long and interesting history.

As for the lens, the ADVANTAGE of a Planar / Xenotar over a similar era Tessar is higher edge performance wide open. At f/8, they are practically the same.

Again, the Tessar is not in any way an 'economy' lens. The limitation of the design is edge performance at a high speed. But unless you are using the camera to make 30 x 40 prints of fine detailed onjects, using perhaps a film yet to be invented, you won't see a practical difference with your T.

Said differently, if you were making your living shooting color images wide open, the Planar / Xenotar would be better. But Avedon never needed anything more than his Tessars from mid '50s Rolleis ( yes, the ones Fred Astaire danced with in Funny Face were Avedon's ! ).

You will find the 3.5F & 2.8F to be faster handling, but no big difference in picture quality. If you enlarged the T's negarive in a perfect enlarger, like a Focomat IIc or a Durst 1200, you'd be able to see a difference between the 3.5 F and a 3.5 T ONLY if you shot a picture of something that made such a comparison possible, like a test target or building. But the T's image would be so good on it's own, you would never notice a deficiency.

Rolleiflex owners have always enjoyed joshing Hasselblad users over the superior results the Rollei TLR gets. And why not, it's that much simpler. Content yourself that your Rolleiflex T is the equivalent of a Hasselblad with an 80/2.8 Planar.

If you want to get a fancy Rolleiflex, get as new a model as you can. The Schneider and Zeiss models are dead even in performance. The 3.5 is a hair better ( an absurdly fine hair ) but a half stop slower. A toss up.

Comparing the late 50's / early 60s camera you have, to the end of the run examples: '70s-'80s Planars & Xenotars, you'll find more of a difference. But hardly a distinction that would make a bad picture good, or a good picture bad.

A thousand dollars is a fair price for a good, user, correctly functioning late model Rolleiflex. An excellent Rollei technician is Harry Fleenor. Contact him to find out a current overhaul price. Then shop for a good camera to fix up. Most Rolleis, like Leicas, haven't been used enough to be reliable today... like leaving a Rolex watch in the drawer for 40 years.

Good luck. You have a real treasure... show us the pictures !