Good call, don't feel too bad about it - it's a pretty common journey many first time developers go through. Sandbox and interactive games always sound good until the complexity builds up.
Anyway I don't think you are the first developer doing conversion or at least featuring VN as the primary mode after starting with sandbox. Off the top of my head Oppai Odyssey and Abyssal Lust are in a situation somewhat like yours.
They started out as sandboxes, then it kind of never lived up to its promise, but in order not to piss of old timers, they introduced a VN mode in parallel.
Pros of doing this is it sort of pleases both sides and allows a "soft kill" of further sandbox feature development, cons is both modes end up sub-optimal.
Sandox mode is low value add just clicking around to trigger events, VN mode is often truncated with unexplained time skips as it simply auto plays out one event after another.
Perhaps you doing a complete conversion will set out a new path. =)