Old Riders have gotten upgrades in the form of new and updated materials being used for their suits. The thematic of the suits themselves has not gotten a redesign, but they certainly look modern in comparison. They modernized them without changing the image.
Outside of suits Riders get new powers and new ways of displaying those powers (except for Kuuga who got a whole new form, but many just say that's Onodera!Kuuga, and the original has no such form), such as X-Rider's treatment in the recent spring movie.
Or small modifications that imply they have gotten an upgrade off-screen, such as Hongo's inclusion of the TRC logo into the belt as Ichimonji had.
And of course, updated Henshin effects.
You know, before Fujioka finally came back out-of-suit, I was convinced they would one day bring AU Riders 1 and 2 (not like THE FIRST, these ones would look the same), or a Rider that has a similar theme as them (such as this #3) to show a modern version of their transformation, because they couldn't (or didn't want to) get the original 2 back.
I think one of the reasons Hongo got the Rider 2 Henshin (with the TRC logo cover and the camera zooming away to show him while the belt produced the multicolored waves, which was a camera angle only Ichimonji got) was because Sasaki might not come back for a Henshin.
And yes, I honestly believe Rider 3 is their way of introducing a redesign version of their suits into "main canon" without having to change their original image.
Personally, I never have been and never will be opposed to a new form for any of the first fifteen Riders (what I have been against is Final Form Rides for them, which is so close to happening after they've already been turned into collectibles and Gaim wearing Rider 1's face in his chest). Giving them a new form in no way disrespects the original image since it's just that, a new form, and it's not a permanent upgrade that will change how they look from now on. Whenever they come back they would be in the outfit they're remembered the most since it's still their default form, just like we don't immediately see Kuuga in Ultimate or Den-O in Climax/Liner. If one day we get Ultimate Forms for all the first 15 that would be fantastic, but I think it would work a lot better if their original actors were involved, Riderman and Stronger exempt of course (Stronger already has an ultimate form anyway!).