I don't understand the Garmin hate. Garmin owns Navionics, and I don't think that (modern) Garmin gear requires a proprietary chart. I may be wrong because my only garmin GPS is a GPSMAP 78, but I run Navionics on it.
Just because you can't get new charts doesn't seem like a good reason to stop using a functional plotter. How often do charts change? How often do you actually update the charts (and your paper charts)?
I use Navionics on my Iphone, Ipad, and laptop (laptop used for planning purposes only, not for actual navigation) and I love it. My Garmin is stand alone (I use on other people's boats) so I don't need to share routes, tracks, etc. with other gear like on my own boat. There have been a number of review of Navionics on this site recently. I'm sure you can find them.
My last comment on old gear. How long do you expect old gear to be used and supported? Five years, 10 year, 20 years? IMHO if you get 10 years from electronic gear then that's pretty good.
Actually, charts change quite often. CG moves buoys constantly, eliminates buoys, and updates shoaling and danger areas. Having updated charts is important when making any kind of extended trip. Keeping up on the CG "Notice to Mariners" is equally important.
I have heard that the Navionics system is good. Some like the charting accuracy better than NOAA charts. I have never had a problem with NOAA charts myself and have travelled up and down the East Coast and ICW a number of times using primarily the NOAA Raster/ENC formats. I have found the updated ENC (Vector) depth charting on the ICW, even through the problem spots on the ICW, to be very accurate and dependable. They are regularly updated. No way would I trust outdated Garmin or any other charts for that. Navigating difficult sections is an exercise in trusting the buoys. It sure helps when you know what is coming up by being able to see accurate charts.
I expect any expensive electronic gadget to be supported until the end of any reasonable expected lifespan. My 376C, a great little unit, still works 100% but is largely useless now because no charts, chart cards, Bluecharts, or any updates are available. I believe 2012 is the latest chart set produced by Garmin that will run on the 376C. We have a throw-away psychology that people have come to accept as normal, such as $1000 smartphones that have irreplaceable batteries or the wonder of the "no flip" mattress. Unless we consumers demand better quality and value, we get what we deserve.