Hm, on further consideration, I believe you're correct. The upgrading functionality is more like allowing the tier tech to advance. Without an upgraded set of refs, you can't produce enough res to pump out higher tech stuff. So, blizzerd is correct in that it tends to increase the slipperly slope. This would be like in Empires 50% of the map could support Lights easily and on occasion a Medium. However, w/ a set of totally upgraded refs, you can field fully upgraded Heavies and then some. However, it does give a nice strategic layer forcing investments to progress. During that investment period, they're more vulnerable. Also, the more teched you are, the easier to knock out their economy by sniping down the refs.
The biggest problem with the whole upgraded ref things is that defending is a bitch! That is the real problem here. It isn't some ref system or raxes. It's defense. Turrets are mostly useless and players often brick stupid. The real problem is clearly defense...
Honestly, maybe the upgrades for refs should increase their defensibility, rather than their output. A long time ago, I suggested putting ammo (and maybe health) on refs, as if they were armories. Perhaps those could appear if they were upgraded. This would encourage even the brick-stupid players to hang out near them and defend them. Hell, it might be interesting if you could upgrade refs into an actual spawn. Have it cost a bit less than building a rax, to reward players for building in a limited, specific location (rather than hiding the rax like they often do.) This would both make them defensible and turn them into staging points for further attacks, encouraging a more natural sort of gameplay where you sweep across the map. Maybe upgraded raxes could count as a sensor for the nearby area, so players who want kills will hang out near them. Just some idle thoughts, at least. These all have the disadvantage of potentially reducing the value of the other building that does that, but of course you could only upgrade a rax in a place where you can already build a rax, while the other buildings can be built anywhere. This would be instead of the res-increase idea, which I still don't think would really work anyway.
I'm not sure if someone has already suggested this, but if you made the cost & build time for vehicles/structures a function of the distance from resource nodes (like it is IRL), building around refineries would become the most cost-effective way to do things, and they would end up being much better defended as a side effect. Upgrading them to produce more and/or faster would also allow pushing out from the base faster and with less cost.
