Valencia CF is going to sell the ground of Mestalla for a about 270-320 Mio Euro and build a new state-of-the-art 70.000 seater. With the money from the ground they want to pay back their debts (120 Mio Euro) and finance the new venue. It will be situated at "Corts Valencianes Avenue" and be able to host Champions League finals as well as trackfield world championships (Valencia want to candidate for 2011) due to a temporary installable running track. 70.000 really is huge. Can't wait to see pics of the new venue.
So, basically, they want to build something using an idea similar to that which led to Stade de France, which is a multipurpose facility that's built to be football-friendly, so to speak.
I don't know for sure, but the idea is similar. The gadget itself might be different. In Stade de France the lower tier is retractable. For football matches it is pulled over the running track, for track and field pushed back. Maybe they use a system in Valencia that allows to build a running track above the lowest tier, thus creating a two-tiered track&field-stadium instead of a three-tiered football venue (that mechanism is going to be used at Wembley, if it ever hosts trackfield events)
It doesn't make sense if you look at Valencia CF alone, but the city and region of Valencia want to use the new venue to candidate for the track&field world championships in 2011 (they missed out on 2009 to Berlin). Plus they really want a Champions League final. And maybe we see what happened very often throughout Europe. That with a new stadium attendance rise significantly. At all, I guess 60k-65k would have done as well.