There is no compelling reason to add a translator over using the panel with the appropriate built in legacy radio. For new sensors I would generally recommend PowerG, and all versions of the panel support PowerG.
I would always recommend using the model which directly supports your sensors.
Hmm, ok. One of the reasons I was considering using S-line sensors instead of PowerG for future upgrades was the Micro-S sensor. It’s a lot smaller and less obtrusive than the PowerG window/door sensor. PowerG doesn’t seem to have any equivalent mini/unobtrusive sensor — besides going the recessed route which just isn’t possible for some types of doors/windows.
But if it’s truly not a good idea to add a translator, I suppose I can stick with PowerG for future expansion and just get the 345mhz panel for the existing equipment.