Given the availability and pricing of secondhand, little-used Psions on E-Bay, I would have thought that 'more of the same' was the best bet. There is still nothing to compare with them for OS stability and a useable keyboard. In addition, the range of add-on software (shareware and freeware) is immense.
I am in the process of accumulating the 'ideal Psion package' - 5MX with full UK and Europe mapping plus GPS and language translators etc., etc. The RevoPlus is an alternative, but less attractive, option.
Pslendid Psion!! - Colour?? Pah! unnecessary gimmicks!