[c-nsp] DCI interconnects at L2 vs Encapsulated spanned Vlan

[Nick Cutting]

>From my words below you will quickly realize I do not really have much knowledge on this subject.  
If you use a L2 tunneling protocol over a L3 DCI - does this mitigate all the L2 risks of a data centre interconnect?
I have only configured various pseudowires in the Lab, and never "tested them nested", nor attempted to introduce a L2 loop on the extended VLAN, and seen what this does to the routed link.

i.e. Would using encapsulation of the L2 frames be much better than for example, running 3 Vlans over the link, using one for routing and 2 for spanned vlans? 

Does this also depend on the type of link the client has purchased- for example if this is a some kind of L2TP / Psudowire - is it less stable to run another encapsulation of the same type (does this even work / MTU nightmares) rather than if this is a dark fibre connection?

Any words of wisdom would be greatly appreciated.

nick