Glenn, I'd say get the 23" now...and as you said, in the long run it will be more beneficial to have two 23". It will be sufficient for a while, I'm sure.
Having dual monitors is nice. I currently have a 20" Dell 2005FPW and a 19" Widescreen Envision LCD sitting side by side connected to my 2.5GHz Power Mac G5. I tend to have multiple windows open at the same time, so having two LCDs lets me use the one for say iTunes and the other for M$ Word, Excel, or Safari.