Making an older race bike more comfortable

I have a 1999 Klein quantum that I pretty much bought because it was pretty and my previous road bike was too big but this one fit me great. I haven't ridden it very much the past few years but now that I am cycling more again I am finding the position is too aggressive for me now.

The bike is in great condition and my husband upgraded everything on it a few years ago to all 9 speed Ultegra with a compact crank. So before I think about getting rid of it and investing in a new, more comfortable road bike I am investigating things I could do to make my Klein work for me better.

Here are my issues:
1. the stem is a 1" quill stem, 90 degrees I think.
2. The handle bars are a little big, when I am in the drops I can't get a good grip on the brake levers but because of the older stem I have not been able to find a more compact handle bars that fit in the clamp, I think it is 25.4cm maybe?
3. Right now I have Rolf vector comp wheels on there that are pretty solid and running 700x23 tires that feel fast but I think need something that will dampen road noise and be less speedy, something that feels more stable.

I have been looking for a stem I can use with a higher rise but being limited by the 1" steerer tube and quill stem I can't find anything that will also allow me to use newer, more compact women friendly handle bars that will give me a Better reach in the drops. Those handle bars all seem to have a diameter of
31.8. Any suggestions? Does anyone know of a good bar for smaller hands that will fit the narrower clamps of an older stem?

I found some adjustable quill stems on eBay and wonder what people think of them. It doesn't solve my handle bar situation but would allow me to try different rises.

I am also thinking about using one of the treadless converter posts and then I could put a more easily available treadless stem with a good rise and bigger clamp diameter, any thoughts on which would be the best solution?

I know I need to at least put on wider tires, if not get all new wheels but there are so many choices! I have read too that based on the specific tire just going wider isn't always more comfortable. What are favorite tires for longer distance rides on more rural roads with lots of hills? Should I go to 25s or 28s?

Thanks for any guidance you can provide. I would really like to try and do a century this year but it will have to be on my hybrid if I can't dial my road bike in for a more comfortable fit.