I don't think I really need 250M (but more is always better)
With the DSO900, more bandwidth is a bit of a double-edged sword. If you enable more than two channels, your sampling rate will drop to 312 MSa/s, so the scope cannot capture signals above 150 MHz anyway due to the Nyquist limit.
With the upgrade to 250 MHz, you have now disabled the analog lowpass at the inputs which would previously suppress frequencies above 125 MHz. So you may see some aliasing -- IF you feed in signals which have such high-frequency components, e.g. fast square waves, AND you have more than two channels enabled.
(Note that using the digital channels will also eat up half of your sampling rate, by the way. So only
one analog channel can be used in parallel, running at 625 MSa/s then, if you want to look at fast analog information in parallel with the digital channels.)