I considered an espionage economy towards the end and was urged to do so by other teams. But I wasn't impressed by the sort of figures I was getting (without actually trying it for real).

I had a couple of great spies available but even with a big lead in espionage over Oyzar (I asuume they hadn't bothered putting much against me!) it was still costing a lot to even steal things like Music. Even with long term stationary spies and about 4000 points I never saw anything I could steal that I could not reserach within 2-3 turns.

It is also more difficult until very late on to gather eps than gold or reserach. With research their are many fairly early multipliers. Libraries & multiple Academies, then Universities and Observatories. Gold is even better with Markets, Grocers and Banks giving you a 100% bonus. You can't get these boosts with Eps until the late game.

Espionage also does not have versions of Wall Street or Oxford. Nor is it a completely sure thing. Doesn't it also depend on the other nation to a degree? If he deploys defensive spies your spies can be found more easily. If he builds up his ep for whatever reason doesn't this effect the cost you pay? These things are not under your control and while you could switch to stealing from someone else the same thing could happen and it will involve some wasted eps.

So although I admit I don't know how to run an espionage economy properly I don't see how it will overcome this point gap compared with straight research and it's other problems? Obviously early great spies can be used to steal multiple techs but this declines towards the mid game and that isn't an EE strategy really.

So for keeping up with researching I am sceptical. Of course espionage has lots of other advantages. In a game which did not have quite as many cities as TTs the sabotage events are cheap and could be effective. It also IMO adds interest and encourages diplomacy as it shows who is getting strong.