A few cents worth
It sounds like three questions: Whats wrong?, Do I switch to EFIS? and why Gyros in a VFR plane?
Why Vacuum Pumps SUCK! 
As you know 3 in-Hg is too low. They need 4-4.5 inch.
Sitting should not be a big deal, at least for the time you said. I know Gyro shops will not let a gyro sit on the shelf for more than a few months with out running it or flipping it over. Apparently a permanent set in the bearings can take, if left idle too long. It sounds as if you just have low Vacuum, so it is the pump or related times (filter, regulator, gauge). However if it was 4-4.5" and now it is lower all of sudden after a period of disuse? May be the pump? May be its a combo of weak worn gyros, weak pump and dirty filter?
Vacuum pumps (dry) are the bane and weak link of the vacuum gyro system. The just don't last. A glasair with a tight cowl can add heat and lower life more. You can expect 200-600 hours out of them. They are just finicky. I guess there are some new companies and designs, but don't know what if any improvement they provide and at what cost. I know wet pumps where much more reliable but where messy.
As far as EFIS. I think you say you are VFR. My feeling is least path of resistance. Why switch to EFIS? Stay with what you have. You have a vacuum system and if it works leave it. Should you pay good money to fix and repair the vacuum system. Well a EFIS is over $2000, but than a few pumps and a gyro overhaul or two is that much. If you did make the conversion you could sell your Vacuum gyros, regulator and pump to defer some of the cost.
Why Gyros in VFR planes
Since you are VFR you don't NEED an Attitude, DG or T&B/Turn coordinator from an FAR stand point, but they are nice to have, especially in a fast cross country plane. If you do any night flying or extensive cross country, I would have want Gyros. Just because you are VFR does not mean you should have zero instrument capabilities (plane or pilot). No, I am not saying VFR pilots should be wondering in IMC conditions, but there are times the gyros will help. There have been several times, especially at night I took off over water, sparse unlit areas or haze and found I need to get on the gyros (JFK Jr. right?). As a CFI/II, I still do VFR flight reviews and instrument comp checks. I spend a lot of time practicing "attitude instrument flying". It is not just for IFR pilots.
Its too easy to get in dark night sparse populated areas that have no ground references. Also cross country you may fly into hazy conditions that gives little ground refrence. So I think Gyros in a VFR plane is not wasted. If all you are going to do is local day VFR flying, I would pull all the gyro stuff out, but a Glasair is a fast high flying cross country plane and gyros are well suited for that mission.
Making the switch
As far as fixing or EFIS switch that is up to you. I don't think you can go wrong either way. How long do you plan to keep the plane? Some people are selling their original Dynon EFIS 10 for later models. I have seen some on eBay. They are great units and could bolt it right in where your AI is, replacing the AI and DG. Keeping the AS, Alt, TC, VSI you would have a nice panel with redundant instruments. I would say if you installed the Dynon EFIS 10, you could do it in about a week part time (10-20 hours?). If you got a EAA buddy who has installed one it would be nice.
You can buy a prefab wire harness. You can use the optional remote magnetometer (recommended) but takes a little more work. I never worked on a Glasair but bet working under the panel may be a nightmare, especially if you have to lay on your back and work upside down. To make sense from a dollar and cents standpoint you would have to do the labor. I have no idea how long an avionics shop would take at $100/hr. Ouch
George
