I'm really not a fan of AUH airport. The lounges are terrible. The same as priority pass and at 1am every lounge was completely full, standing room only. No fasttrack security/immigration, no real fasttrack boarding (usually becomes a scrum). I'd go DXB just to avoid that.

I think the optimum is to buy a W flight to DXB and UuA the outbound J. Although, as you said, £1k is a steal for F. Maybe do that.

FWIW, taxi costs around 350 AED (£70) from DXB to AUH and presumably vice versa. Little bit more from downtown Abu Dhabi. Figure an hour and a half, give or take.