I've got a 36V adjustable supply, and I can't remember the last time I had it over 18V. I know I've had it up high to test the supply and my meter, but other than that, I don't think I've had a practical reason to take the voltage up high. If you're playing with digital, computer stuff, radio stuff, and low power audio, 18V will probably cover your needs for quite a while.
Yeah, RS232 uses +-12V, but I generate that from +5V using a MAX232.
If you want to work with high power hi fidelity audio, you may eventually want a split supply of higher voltage.
One other thing that comes to mind: Many laptop computers use a 19VDC input. Your 18V supply won't quite work to power one. That probably doesn't matter much, unless you're designing or testing laptops. Or if you lost the laptop's power brick, but in that case you should just go pick up another, rather than tying up your bench supply.
Since you mention ham radios, note that they often use voltages much higher than 14V, at least internally. A typical VHF mobile radio transmits around 50W RMS into a 50ohm load, so it's got to be generating 50V RMS on its output, meaning the peaks must be about +/- 70V. But those typical VHF mobile radios only require input voltage of around 14VDC to generate that output. Transformers are wonderful things, no? Anyway, if you're going to power ham radios in the 50W to 100W output range, you'll want a high current supply of around 13.8 to 15V, maybe 15A or more. You don't need the full adjustability of a that bench supply. Horses for courses.
But for general purpose digital and low power analog, 18V is very useful, probably more than enough. I'd go for it.