I went through this exercise in detail about a year ago and ended up with a 530 and 155 in the panel, the 155 giving the route and textual data that you are considering getting off a second 430 and also driving a IIIc Tracker on the yoke.
IFR is based on the 530, VFR assisted by the IIIc. Works well for me.
Totally agree about HSI...an absolute must. I would also suggest an electric AI as a backup.
Go for the wonderful Garmin audio panel.
There is an excellent ADF indicator which behaves like an RMI, but is actually driven from the HSI and therefore is relatively cheap.
Don't forget the Mode S. Again, the Garmin unit is good.