You're exactly right about LCD's changing (or making more complicated) our decision making process when upgrading. The main reason for that is due to the technology of LCD's. The pixels in them are painfully obvious, opposed to the 'smoother' or more 'blurred' pixel definition on a CRT. That's not necessarily a bad thing, IMO. I currently have a 17" Sony LCD @ 1280x1024. I prefer to have ClearType turned OFF in Windows because the crisp, pixel-defined text is easier on my eyes. I really hate that anti-alias text look when in regular 'desktop' mode (i.e. web surfing, email, generic Windows tasks, etc). However, when gaming, I believe this is why anti-aliasing is more desirable on an LCD. In a gaming context, you don't want to see pixels (or 'jaggies'), but instead want to see a smooth, yet crisp, appearance. Unfortunately, AA really taxes even high-end graphics cards. On CRT's, the pixels aren't as clearly defined, so AA isn't as needed (it's still a subjective question, however).
Also, there's something that isn't talked about much (if at all) regarding LCD's and that's dot pitch (or pixel pitch). It matters more now on an LCD than it does/did for CRT's because, as I mentioned before, LCD pixels are VERY clearly defined and seen. This is something that may actually help you out in terms of making text easier to read for your 'mature' eyes
Take, for instance, your LCD (20" widescreen with a native resolution of 1680x1050). In order to fit that number of pixels into that physical screen size, each pixel is actually 0.285mm. Now, compare that to another 20" LCD (also a widescreen), but with a lower native resolution (1400x1050) and its pixels are each 0.292mm in size. So, you have the same physical size screen (20") in the same proportions (widescreen/16:9), but the pixels within the screen of each one are a different size. Another interesting comparison is the 17" vs. 19" LCD. Many people think that a 19" LCD is 'better' because it's bigger. However, most (if not all) 17" and 19" LCD's have the SAME native resolution (1280x1024). This means, in terms of the pixel pitch, that the 19" simply has larger pixels than the 17" (0.294mm > 0.264mm). So for someone who prefers to have their text and overall screen readability larger (i.e. you), the 19" is the 'better' monitor. For someone who simply wants more 'screen real estate' (literally I mean more pixels on the screen so that the net result is being able to 'see more' of your Windows desktop), then there's NO difference between the two monitors at all! This is why I bought a 17" instead of a 19" 3 years ago. I really wanted a native resolution of 1600x1200, but those LCD's were way out of my budget especially 'way back then.' So I opted for the 17" since it was the most economical decision and didn't offer me any less in terms of 'performance.' (I am, afterall, a resolution-monger! I'm all about having more pixels )
Anyway, that's just something to keep in mind in case your current monitor ends up getting too hard on the eyes. BTW, my new Dell 24" (native resolution of 1920x1200) has a pixel pitch of 0.27mm, definitely smaller pixels than your 20" but larger ones than my current 17" LCD! I always find the pixel-pitch and native resolution stats to be interesting for some reason. Take care!