Agreed, for flying IFR.
When I got my Instrument rating, GPS existed but most GPS approaches were just "overlay" approaches, where the primary navaid was still a VOR or NDB. And the only vertically guided approaches you could do were ILS approaches, which are few and far between, especially at GA airports.
Today, nearly every little podunk municipal airport has RNAV approaches, and a large portion of them have LPV minima. It's like having ILSs all over the place. An engine failure in IMC is FAR more survivable today with a WAAS GPS than it was back in the day, and for everyday operations, having a nice stable LPV or even +V approach is far better than a VOR or NDB approach was.
With the advent of more reasonably priced units like the GPS 175 that give you full WAAS capability at the entry level end of panel mounts, it's hard to justify not having a panel mount GPS these days.
I know and agree. Installing a GPS 175 costs about 10 AMU all in (parts, labor, etc.). Just because it's the cheapest doesn't mean it's "reasonable" - that depends on whether one actually uses it.
There are a few reasons why I am earning my IFR without a GPS or autopilot.
1. My primary goal is not for any practical use, but only to lean more and improve certain skills. After 18 years and 1700 hours of flying all over all the places in my sig map, all VFR, I know I don't need the rating to do the flying that I like to do.
2. Getting the rating with no autopilot or GPS means true competency. We occasionally read about IFR pilots who lose the autopilot or GPS and die within moments. They became automation dependent and could not fly the airplane on their own in actual IMC. This shouldn't happen, due to currency rules, BFRs and IPCs, but it still does which means this kind of "deviance" is sometimes "normalized".
3. This reminds me of one of my CFI's friends. He was a young man who trained for his IFR in a glass panel airplane with autopilot. His Dad (a professional pilot) was sponsoring him. When he was ready for his IFR checkride, his Dad made him repeat the training in a steam gauge airplane (equipment SD) having no autopilot, until he could fly that as well as the glass panel. It took him another 30+ hours flying that way to become proficient - which he did, passed the checkride and continued on. The skills he learned might save his life some day.
4. I already have a Stratux with ADS-B In, a GPS, a tablet with EFB software having full VFR & IFR databases and geo-referenced IAPs. Because of this, a certified panel GPS provides no value for my normal VFR flying.
In short, I know the GPS greatly increases the capabilities of IFR flying. But it does nothing for the VFR flying that I normally do, and I don't need it for the IFR training or the checkride. So I'm deferring that decision until I know whether I'd get any use out of it.