According to the Spanish secretary of state for European Union affairs, Diego López Garrido (cited in El País), in an ideal situation the Lisbon Treaty would be ratified early enough so that it could be applied for the upcoming European Parliament elections. The reason he presents: Spain receives four more seats under the Lisbon rules compared to the present (=Nice Treaty) situation. If Lisbon enters into force too late, the four seats have to be added at a later stage.
I am glad that some politicians are as open as this. Why talking about common values, balance of powers, or the possibility of future enlargements? For Spain, the timing of the ratification of Lisbon is as simple as the calculation x + 4 = better then x (while x would be 50 according to Nice). Politics are much nicer if you keep them this simple!
(To be fair: López Garrido also adds that with the Lisbon Treaty the Union would gain in legitimacy thanks to the strengthening of the Parliament and the inclusion of the Charter of Fundamental Rights.)