I have an old '74 Chevy C-10 for a work truck and a couple years ago I put an Edelbrock Performer cam and intake on it (used the original Quadrajet) and I've been very pleased with it . . . it inscreased my mileage significantly, I was getting 10-12 with it before the swap and I get 16-18 easily with it now and I have got 20 with it but it's not fun if I drive it that judicisouly!
Of couse I must admit that it may not be all attributal to the cam and intake . . . while I had it apart I replaced the points distributor with an HEI (with new cap, rotor, plug wires, and plugs) and I rebuilt the Quadrajet. The heat crossovers in the old manifold were plugged with carbon, etc..
Sooo, it got a new cam and lifters but also got a super tune up at the same time.
The mileage is livable now and I really like the power band of the Performer cam, though the old cam was so shot that I really didn't have a good baseline to compare it to.
In a car as light as a T though I'm not sure you'd really notice just an intake change (assuming you went to a similar dual plane design, a single plain, hi-rise, etc. would probably make a noticable difference but I'm not sure it would be a positive difference as far as drivability).
Personally I don't think I'd spend the money on it if you were counting your pennies on the project. If you like the looks of it or something and really want an aluminum intake then Youngster is right - check the local swap meets, your local Craig's list, etc. as you can usually find a good deal on a used aluminum intake.
Dave Vizzard in one of his books give a part number for an aluminum intake that was stock on I think mid-80's Monte Carlos and stuff and he said it worked about as well as an aftermarket one. We picked one up off of FleaBay for a little of nothing. It came painted corporate black, but we just bead blasted it and it cleaned up nicely and it worked on one of my son's projects just fine. Youngster is right though, FleaBay is a gamble since you can't examine things before you buy and aluminum is easily stripped or beat up. I'll see if I can dig up that part number for ya (you got to be careful as Chevy changed the angle on the heads in the late 80's I think so you need to get one that matches your heads).
TTYL,
Steve