There are certainly many more benefits to street trees than simply looking nice, for example:

• Reducing pollution
• Reducing road noise
• Providing shade from the sun - mitigating 'urban heat islands'
• Absorbing rain water and contributing to 'sustainable drainage systems'
• Acting as a buffer from high winds
• Providing 'traffic calming' & reducing the speeds of motorists
• Becoming a habitat for wildlife
  

The point about potential damage to the pavement & foundations is definitely a valid one and one which needs to be considered whenever a new tree is planted. Fortunately, as this is an issue for councils across the country quite a lot of research has been done on how to mitigate these risks - e.g. see http://www.forestry.gov.uk/fr/urgc-7evbwr from the Forestry Commission.
One of the solutions is to install 'root directors' surrounding the tree pit to ensure that the roots go deep enough before extending out horizontally:
   

Regarding the bird mess, I acknowledge that this is a potential issue however I don't think that it is sensible to base any tree planting decisions on this, after all we do not live in sterile environment and will always share it with wildlife. E.g. What about the birds that fly over your car now? Or the cats which won't think twice before jumping on your car? Or the Saharan dust etc. etc.

Finally, Sherwood points out that trees can block street lights. This is another very valid point and one which is definitely considered when choosing a suitable site for a new tree. (Also I'll add that I believe when Skanska redid the lights in Forest Hill it was the lights which were badly placed rather than the trees! )