Spain is awesome. I'm currently working on a big article about them for the strategy section. I consider them one of the best civs to try to beat Deity with - provided you get a re-roll or two if you really strike out on Natural Wonders.
At a worst case, you get 600

and +6

in the first half of the game. Absolute worst case, assuming you bother to explore. Take your

and buy a CS ally and you basically get a free Notre Dame, plus any units,

, or

they provide. Powerful stuff.
Average case, you find one Natural Wonder first that is kind of at the periphery of your natural lands. You will have 1000

in the early game, +6

, and the option to settle near that tile. The weakest Natural Wonders will give you about as much as an academy, manufactory, monument, or customs house with the 2x modifier. Settling Barringer Crater, for example, is more powerful than Babylon's free academy, since you also get

from it too. Plus, you know, all that

.
Good case, you find GBR, El Dorado, or two NWs nearby. You will be rolling in 1400

pretty early and +6

. That lets you buy workers, settlers, tons of units, libraries for a 2 or 3 city NC start, or pretty much anything your heart desires. Two free early

allies makes boosts like France's seem pretty weak. And of course, you can often settle those tiles, getting the major

,

, or

boosts. You can be both rich and teching like mad - a recipe for victory in any circumstance.
Plus, Spain gets two pretty solid UUs in the midgame. Considering that you will have a

and

advantage in getting off the ground and a military advantage in the midgame, that should deliver you to a winning point by the time your UUs and UA start to dilute. And this dilution effect over time can be said about a lot of Civs.