I generally agree with Will about running costs. V6 is quite problem free and the gearbox (yes, only automatic is available on that) is very reliable in the 24v engine (12v engine is also problem free, but gearbox requires overhaul every 150.000 kms or less), so you should not be afraid of complete breakdowns. 12v V6 has chaindriven cam shafts so there is no cam belt to replace. 24v V6, however, has a cam belt and it requires the engine to be removed from the car to replace it. It is therefore very costly.
2 litre petrols are also quite problem free, but stay away from the automatic variants. They also have cam belts, but are quite easy to replace.
Diesels are excellent powerful engines, especially the DCI'engine (later models), but I've heard about some reports of turbo failures on the DCI's. Actually it's the bearings that fail and this causes the engine to run on engine oil - unless you have the luck/nerve to force it to a stop using the brakes it will destroy the engine. Diesels also has belt driven cam(s) but should also be easy to change.
I dont agree completely with Will that you should stay away from Renault garages generally. I think I know what he means though, and here in Denmark too the larger Renault garages generally gives a bad impression. They do have one advantage though, which is that they have the proper testing equipment for your car, which is absolutely necessary to diagnose and fix more complex errors. My Espace v6 24v developed a fault on the enigne and on the gearbox. Neither were serious, and the fault codes were simply deleted by the garage - but now we know what to look for, and if/when the problems we have experienced start showing up on a more regular basis, we will have to fix these parts. An independent garage would not have been able to do that.
Electrical problems are common on Espace's, and some problems may be hard to fix. In Germany the Espace tops the statistics about on-road breakdowns - and as far as I know, most of these are due to electrical problems. My own experience, however, is not that bad - I have only a courious failure on the outside temperature sensor, that shows about 12 degrees to little. We get some funny comments by passengers on that.
That was all the bad news.... the good is that the Espace phase 3 (1997-2002) was extremely well built with glass fiber body and warm galvanised chassis. You will NOT see rust problems in one of these - except in the engine hood, which is metal. It is also very beautiful, but you already know that
Another is that it was the safest MPV with a four star rating in Euro NCAP crash tests. This was revolutionary by the time it was first tested (1998) and is still today an acceptible rating. DON'T FORGET to tie down your bikes to the floor, however!
Hope this is of some help in deciding a variant for you!