I found that my Titanium bike frame didn’t last forever, as I thought it would. It was a Litespeed that I put about 25K miles on over 11 years. A trusted mechanic did a short test ride at that point , after a repair on it and noticed it was “feeling its age.” It had literally developed metal fatigue. I tried a newer Litepeed, and he was right. Then I found out how much carbon frames had improved in the interum, so got Carbon instead this time. 4 years and 10k miles later, I still love my economical Cannondale carbon bike. Its about the same weight as my 2004 Litespeed, good enough for me, great frame feel and comfort.I don't think you're missing much at all, and if love riding your bike then why get a new one? Do average riders really need 21 gears instead of 10 or 12 or 14? nah! but I see you upgraded yours to STI, personally, I would not have done that with your bike, but that's just me. The bike you have you can't get anything similar new today without ordering a custom-made bike and that will cost you a lot.
If you are still thinking about getting a new bike I would not buy an aluminum bike, they have limited life expectancy depending on how much you ride it, and you won't like the ride of it coming off of a fine bike like you have now. You will also experience a sort of deadish wood like feeling to carbon fiber compared to what you're used to, also with carbon fiber if you crash but don't see anything wrong with your bike you could have something wrong but the damage is most likely internally and may not be visible from the outside, so then you have two choices, take it back to the shop and they will send it back to the factory to be x-rayed at a cost to you, or take a risk and ride and hope there was no damage and it doesn't break all the way while you're on it. Also with CF frames, you have to make sure you know the correct torque values for everything you put on it if you don't get the value right and over-torque something you can crush the CF tubing which will lead to failure. I found it a bit disconcerting when I was able to press in a CF top tube with just my index finger and thumb.
If you like your steel bike ride comfort, and you know steel is very durable, then I would suggest you look at titanium instead, it's a long-term material like steel is, and it will actually ride a bit more comfortably than your old steel bike did! Yes, TI is expensive, but I know you won't be buying another bike for at least another 30 years, so figure out the cost per year of having your old bike with inflation factored in, and then do the same thing with the cost of TI. With TI you still will have the drawback of CF fork but with forks like Enve 2.0, True Temper extra-thick steerer tube version,