Some quirky Ecclesitheurge gishes:
Asmodeus: Fire primary to get scorching rays, fireballs, and controlled fireballs. Later fire domain spells kind of fall off, although you get some quirky things like weird and fiery body at 9th. You get cloak of dreams, confusion, fear etc. Trickery as second domain for a poverty mirror image as a move action and mass invis as a free action.
Gozreh: Weather gets absurd at higher levels. Siroccos, Firestorm at 7 instead of 8, etc. You get strong druid stuff while keeping whatever cleric tricks you wanted. Also gives you call lighting as a swift action as it's domain trick. Ends up being handy for finishing off enemies with 10 or less hp, which comes up more frequent than you would guess. Water gives you stinking cloud, cone of cold, horrid wilting. Air gives you lightning bolt, shout, cloudkill, chain lightning, greater shout. And you can even take animal domain and a pet if you'd like. It's the most munchkin deity out there, I think.
Erastil: Desiderus Community domain gives you this epic once per day sacred bonus to attack rolls and saves equal to your wis bonus. You get long bows as your favored weapon. Can get a doge. Legendary proportions and communal stoneskin.
Torag: Lead blades, barkskin, seamantle, disintegrate, waves of exhaustion, acidic spray, horrid wilting. It would be cool if blessed weapon was an artifice domain spell, but alas.
Lamashtu: Frightful aspect, cloak of dreams, legendary proportions, a bunch of enchantments that target will saves that your bard probably already has, and madness has a free action mass enemies only confuse. Also get the trickery mirror image and mass invis.
You can also dip in traditional monk for most of these if you hate fun.
tl;dr: Gozreh gives you a lot of fun spells and an optional pet. Other deities have a cool trick for a gish or two.
Anyways, while not quite the same, Ecclesitheurge is kind of fun for the same reasons as your hypothetical double thassalonian because you have to be a bit more creative to make the most out of your arcane domain spells as opposed to just defaulting to the best in slot arcane available at each level. Many of the domain abilities are also some of the more interesting abilities in the game, IMO.