Several questions
 

I ride a touring bike with racks, fenders and panniers and ride with a group of 50 to 70 year olds like myself. Many of them ride 19 to 20 pound road bikes and after 20 or so miles I find that the faster ones start pulling away from me. I removed the racks, fenders and panniers and took off the touring tires and replaced them with 700 X 28's which is the narrowest tire I can put on my wide rims. I managed to lighten my bike by about 6 pounds. This added about 2.5 MPH to my average. I can't ride a road bike with drop bars due to a bad back so I have to use flatbars with bar ends. My rear wheel spacing is 135 and I understand that a road bike rear wheel is spaced 130. Is this correct? I have some 10 year old mountain bike (LX) hubs that I could have built up with narrow rims so I could use an even narrower tire. Would this help? I don't want to spend $2000 or more for a new bike. I am a big guy (195#) and wonder if a new wheelset with 20/24 spoke wheels would hold my weight. Or is a new bike in my future? Any other ideas? Thank you, Rich

Road-racing bikes use the 130mm rear axle, yep.

Part of your speed increase is due to the lower air drag of not having racks, fenders, panniers and wide tires, not just the lower weight alone. You may already have reached the point of diminishing returns without spending much money yet :) If your back weren't an issue, then an aero bar might be worth trying, because it helps streamline the rider, who's the majority of the air drag. And air drag is what slows you down most when you're on a steady cruise.

If you do try aero bars, get ones where the armrests are behind the main handlebar, not right over it, and consider using a shorter, taller stem if you find you're too hunched-down. Also, leave a big buffer of space around you since they make the bike steer differently when you're down on them. Worst-case scenario, you can unbolt them and sell them off to your pals if they don't work out.

Syntace C2 Ultralight, I have a set of these.
http://www.nashbar.com/nashbar_photo...um/SY-HBC2.gif

For me, the aero bars give 1-2mph boost when I'm just cruising the highway, with no additional work, and I just sort of drape myself between the seat and bars and relax my back. That's a bigger boost in speed than my exotic $1200 all-carbon Zipp440 tubular wheelset was, back in the day, and for a bargain price of ~$100. Although those Zipps were wicked-cool and accelerated really well... :D

I just got a roadbike off Ebay for $15. Just needs a new cable, a two new tires. Total cost, $50. No reason you couldn't do the same.

There are millions of bicycles not being ridden, just laying around. No need for anyone to buy a new bike.

You could build up the LX hubs with Open Pro rims. This would be reasonably light and accept 23-28mm tyres.
If you want to get more aerodynamic, think about width as well as hight . Some Spinnachi style mini clip-on bars or small aerobars would bring your arms in and eliminate the parachute effect.
Is is possible to set roadbars higher than a race bike. This would give you plenty of alt handholds and maintain your more upright stance.

You could realize that while slower, your touring bike is infinitely more practical and useful than a silly racing bike. They may outrun you after a while, but there are places they can't go and things they can't do on those expensive toys.