Kinda depends on the age & condition of the 430. A 430 WAAS in good shape with a perfect screen has some life left in it. A non-waas unit, or one with screen issues, becomes a high priority for replacement.
The 430w is waas and is in great shape. Not sure of age but they stopped production in 2011 I think, so at least that old. I'd have to go through docs to see if it was new, or used. My thoughts for upgrading it is the apparent limited support life of it, it's declining trade in value, and everyone's rave reviews about the Avidyne.
New COM and audio panel would be a great upgrade, modern audio panels have a much better noise floor and a whole lot more features. One option for ADS-B in/out would be pairing a GDL-88 with your 327, they can be had fairly inexpensively and will interface with the 430W for traffic display. Certainly a GTX345 or GNX375 are nice options, but you can pick up a GDL-88 for around $1.2k.
I'm going with Dynon brand, so I'll likely put in the Dynon transponder\ADSB unit to easily interface with the HDX. Although I'm not sure if others will or won't interface with it.
I'm planning on riding my GNS-430W until it dies. They are very robust. Having a reliable #2 NAV/COM is your insurance against a GNS-430W or GPS failure if IFR. A modern audio panel can make future avionics upgrades simpler and adds some nice features. But like you if the GNS-430W dies it turns into an IFD-440. I'm in the same boat with the #2 NAV/COM. Works, but not pretty and the sound is eh?
The Com I'm looking at has no nav, so it wouldn't be a backup nav for the 430. Sad, but true. One of the little things that keep going around in my head. If the 430 craps out, I can use a GPS backup like the Stratux, iPad, phone, etc...unless there's an outage or I'm getting jammed. All happening when I'm IMC...which with my luck, is quite possible lol.
Have you looked at the used market for the second nav/com? Maybe something newer, nicer that got replaced in a full panel upgrade.
I am leaning to the side of, if you 430 is WAAS and working well, start with the other parts until you NEED to do something about the GPS.
Haven't looked much at the used market yet, as I'm just now getting serious about upgrading.
All great thoughts/replies.
The general feedback seems to be hang on to the 430w for now. I'm sure that will cost me later, as 430 value goes down, and cost of 440 goes up, but, never know. Maybe there will be a sale
One of my main thoughts, is do the upgrades to the Audio/Com/Transponder while we have the panels out. The 430 to 440 wouldn't need any panels removed or additional wiring (I'm assuming).