It depends on the capability of the navigator but in your example, if only a 430 is properly installed, It is adequate to use as the sole source of navigation. (Edit: see RAIM requirements Sam posted also)
However, the way I read the regs, if an alternate required, alternate weather must permit a VMC decent to landing from MEA. A non-waas GPS may be used as the sole source but both destination and alternate can't be based off GPS approach, so if you're using a GPS approach at the destination then it has to be VFR at alternate and weather must permit a decent in VMC from MEA.
I have a WAAS GPS as the sole source. I do not have a panel ILS/VOR at all. I do carry a backup Yaesu FTA 750L, that is connected to an external antenna and is for emergencies only, and I practice ILS using it. It's not pretty but it mitigates the risk. There were several factors that made me comfortable with this, one of them being I have an AP that is as capable the airplane I fly professionally