I am not an expert but I drove my cousin's EP while I was at Tokyo during the 2011 Auto Salon and I owned a DC5 myself. I drove my mild-MOD DC5 daily with FC on average 11-12 km/l. On highway the score will be much better at 13-14 km/l.
Space
I'm quite surprise that EP has more space interiorly than DC. DC has lower head clearance especially for rear passenger.
Boot space - of coz DC's bigger and accessible from rear passenger (if you dont have the rear boot cover). Front recaro seat, EP - comfort, DC – hard n more body hugging.
Comfort
It’s all depending on how u setup ur car. My coz EP is all about comfort and just a bit on performance. He uses complete Mugen setup (non-adjustable) for the suspension while I'm on hardcore fully adjustable system. So you can imagine how diff both cars will behave on the road.
Performance
I dont know guys, but I felt just a soft-kick of Vtec while I'm on my coz EP. It is not the same what my car will roar when the Vtec kick-in. Again this maybe resulting from fully Mugen exhaust system on my coz EP (twin-loop) and mine fully customizes system with loud Apexi N1 end. Both still using the same virgin comp box, and both still have the same rev n speed cut. It is not just about the noise, but the fell.. felt more kick on DC.
It’s true what affiq said, being a rare creature, it is hard to get parts especially bodypart for EP. Even harder to see anyone selling it right now. Just look inside ZTH, u can find a lot of DCs selling while EP is rare (or none). Yes Kamarul was selling his a few months ago, but in the end plan to keep it.
If ur friend does have another car for the family, then a 2 door coupe is okay to have. But if he is going to use the same 2 door coupe, I don’t think it is a good choice. And by the way, for the passenger, getting in and out of DC is harder than EP.
I was only able to experience 2 weeks with the EP (Tokyo's traffic jam, touge attack and Wangan cruise at night) so maybe my judgment on EP is a bit bias. Maybe EP friends can correct me…