Is there a specific reason you want a Nav radio for VFR-only flight? I fly VFR and IFR and have not used my Nav since I finished my instrument rating. I am only putting a Nav receiver in my homebuilt as insurance for GPS outages, and it was a major struggle to make that decision because the only use would be for GPS outages. I couldn't find an airport I wanted to go to that had significantly lower minimums for the ILS than the GPS approach to the same runway.
Same question for the second radio: What is your reason for wanting it? I fly a lot of VFR using a single radio with the capability of monitoring a second frequency. My plane with two Comm radios doesn't have that feature, so I use the second radio to listen to ATIS/AWOS and to monitor Guard on long cross-countries. I could easily live without it if I had standby monitoring on the primary radio.
As an airplane shopper, I would rather see a 182 that is equipped for GPS-only IFR than one that has a Nav radio. I think that the only hope of recovering part of your avionics investment is to maximize the target market of your airplane in the event you decide to sell it. No, you don't plan to sell it today, but if you can make this asset more readily liquidated you will have a little bit more buffer against unforeseen lifestyle changes.
You may prefer using the Aera to an IFR GPS. I haven't used an Aera 660.
What I would look into doing is a GNC 355A ($7,700) and Aera 660 ($750) with cross-fill, and leave room in the panel for a GTR 200 ($1,200) if you can't afford to put it in now. Drive the autopilot from the GNC 355 to make it easier to use under IFR. (You can save $700 by using the GNC 355 without 8.33kHz channel spacing, but I assume you need that.)
This comes to $9,650 in radios if you get them all now. The list price of what you are thinking about is $4,500 for the GNC 255A, $2,100 for the GTR 225, and the same $750 for the Aero 660. The total is $7,350. The list price delta is $2,300 and the capability delta is an IFR GPS instead of a a Nav receiver. It's your money and you should spend it to make yourself happy. But I do think you will get the $2,300 back if you ever sell the plane due to the huge increase in IFR capability, which will find more buyers as well as justify a higher sales price.
Note: I assume you have and are keeping either a two-needle CDI or an HSI in the plane, to be driven by either the GNC 255 or the GNC 355. I also assume you have and are keeping your standard six-pack instruments.
