If I recall correctly, I've heard Stein give ballpark quotes of $20K VFR, $40K IFR.
But for a number of years, I flew a gorgeous RV-8 with steam gauges but with a small panel-mount GPS and an R-9A that was all glass. My question is, why do you want to change?
Steam gauges are more readable than glass, primarily because they are larger. The one exception is the attitude display on glass is bigger, which helps in roll, but the pitch scale is not necessarily larger. Round dials are as readable or more readable than tapes, the biggest advantage is that round dials are much easier to read at a glance.
When I fly glass in the -9A (still have it), the autopilot keeps the plane going in the right direction so I have time to fuss with all the button pushes of the glass. In the -8, because it had more sport plane handling, it took a lot more attention to keep it precisely on heading and altitude. Flying with an autopilot in a -8 seems to me like having a chauffeur drive you around in your Porsche.
Another factor is whether your -8 has a cutout in the back of the forward baggage compartment to access the back of the instrument panel. I do not know how big a project it is to add that after the fact, but that can be a big deal for accessibility. Then again, if your glass cockpit has a 10" screen or two, removing that screen solves lots of accessibility problems, especially if you have a generous service loop.
Then there's the matter of workload. As mentioned above, in the -8 I spent time flying the plane but in the -9, the autopilot gave me time to fuss with the glass (and most of my flying in the -9 is either IFR or VFR using IFR procedures.) I've found it quite challenging to hand fly the -9 and attempt to use the glass in the same way that I fly it with the autopilot.
As for aesthetics, that's certainly a personal choice. The -9A seems a good fit for glass, two screens plus the GPS navigator. The character of the -8 seemed more appropriate for steam gauges, the fighter aura, all that.
The one true advantage of glass is hazard avoidance, whether that hazard is traffic, weather, airspace, or terrain. Glass does that, steam gauges do not. My -8 had an older portable GPS panel mounted, so I experimented with my older iPad. It was a minor hassle putting the iPad on my knee as it would quickly overheat in the sun, even if it was turned off. What I did was to turn it off and put it beside the seat vertically when I wasn't using it. (When I had the high wing Cessna, the iPad was much more useful).
Bottom line -- if you've got a nice steam gauge panel, enjoy it, and figure out a strategy for a hazard avoidance, whether tablet or small panel mount GPS.
Ed