The real problem seems to me not the warp scale, but the writers want to one-up the previous speed champion too often, resulting in stuff like a 10-fold increase in top speed within a decade. There will be no real solution until they curb their enthusiasm for that and restrain themselves a little more.
It's not as if they need much higher top speeds anyway (well, apart from Voyager that needs to return from the DQ, but they arrived there by highly unusual circumstance). There's a Galaxy out there with 400,000,000,000 star systems, the exploration of which will take them centuries even for an organisation the size of Starfleet - unless you assume a steady exponential growth of their numbers and new member species. Being able to zip through the galaxy in minutes doesn't significantly speed up that effort, the actual exploration will still take the lion's share of time.
