Here’s a good article by Barbara Bodine, former US Ambassador to Yemen and director of the Scholars in the Nation’s Service Initiative at Princeton University.  She argues that the next president should stop the practice of filling over 30% of ambassadorships with presidential appointees, those loyal to the party or to campaigns.  The positions should instead be filled by career diplomats.  I think her article makes some good points but I would also add a few things:   
 
Public engagement: Everyone knows by now that the US has a pretty bad reputation abroad.  Public diplomacy is on a decline.  Under-qualified Ambassadors risk embarrassing cultural faux pas, (such as the recent US Ambassador saying “God Bless Germany” in a recent speech).  Come on...
  
Competitiveness: In a “Post-American World,” the US needs these relationships.  The US share of world GDP has been shrinking since WWII, our infrastructure is struggling to maintain competitiveness, and experts talk about a multi-polar future.  In short, the US needs to play its cards right in order to maintain power, and high-quality diplomacy should be part of this new strategy. 
 
Urgency: No, one cultural slipup won’t damage relations with a loyal partner.  No, the UK will not suddenly abandon the oldest friendship in the world for a closer partnership with the Chinese.  The US still enjoys a strong reputation abroad, but distrust is deepening.  Sloppy management of relationships −even historical ones− could lead to a slow and quiet drift of allies and undermine previous areas of cooperation that previously reinforced America’s standing: military collaboration, international development cooperation, and economic trade.

I'd be curious what our current YPFP Delegation in England thinks about this issue...

Further Reading:
The Future of American Power
Public Diplomacy: Reinvigorating America's Strategic Communications Policy