I'm not saying the new technologies are a must have especially trolling deep water but they certainly are valuable for some situations. DI is amazing for seeing fish belly down on the river bottom where even the best 2D sonar has difficulty separating them from bottom. DI also makes it easy picking fish out of thick weeds or brush. Sidescan is a great tool trolling musky and finding schools of baitfish or perch. I never run either walleye fishing in Erie but I regularly use both for the other applications. Are they really necessary, no, and for many people they are of no use but it depends on what you're doing.
The other important thing is to learn how to use whatever electronics you buy effectively. Every different situation requires different settings to get the best info out of them. This takes some time and effort but there's lots of you-tube vids and on-line resources to help out. To me it is pointless having someone 'set-up' your unit unless the settings are intended for exactly how you're fishing, they need constant tweaking for fine tuning things. As somebody once told my, it doesn't matter how expensive a guitar you buy if you don't know how to play one....