What I find hard to understand is how Lufthansa, Air France, KLM, Swiss, SAS, Turkish and to a lesser extent TAP, Finnair and even Icelandair can offer multiple daily services to their various hubs from UK regional airports, yet somehow Iberia can't fill x9 CRJ's a week?
Although the latter three you mention don't fly to BHX the others all do well from BHX and other regionals because they offer multiple interline opportunities to a host of cities in the Middle East, India, SE Asia and North America. MAD with IB would only really is useful interlining to South and Central America, still emerging markets for Europeans in terms holiday/leisure traffic at least. FRA, MUC and DUS with LH have strong business links with Birmingham, with good O&D traffic levels, CDG and AMS are strong on city break traffic.
Always though it was utter madness at MAN to go from none to three airlines to MAD and all within a few hours of each other! At least it knocks the BHX-MAD rumours on the head with IB. Depending on success of IB Express they could be possible in the future to serve MAN, BHX maybe GLA but they use the A320 which is a big old bird to fill profitably on a city route from BHX at least.