The short answer is "NO" as if there is no chance of you flying in IMC then you can quite leagaly stay VFR and all you need for that is a compass, map and stopwatch.
However I suspect that the class 2 IR or something along those lines will show up sooner or (probably) later, if this comes to pass you will have to get FM immune.
I think in your position I would wait and see because the cost of the new kit is coming down, the latest offerings from King undercut Garmin and from the spec look better (personaly I prefer the King kit as it follows the same logic as most FMC's).
Added to that If you want to fit the new King kit I will split the paperwork costs for instalation in a DR400.
https://www.bendixking.com/whyBendix...Bendixking.jsp