Peercoin's light blockchain

A question:

The benefit of peercoin is that it has a lightweight block chain (e.g. the transaction fee prevents frivolous transactions, as does the minting reward)

There have been a couple of proposals to build on top of the block chain (Jordan’s voting motion and the PPC version of Counterparty). I think a few people here commented that these will add weight to the block chain

My question is: what is the point of keeping the block chain lightweight if we do never build on top of it? Iif we never build on the block chain, what is the benefit of having it? Can it develop and remain lightweight?

With sidechains - yes.