First off, if/when Bitcoin takes off for real there's going to be nerd cred to be had running a node. And terabytes of what you call bloat only makes it better.
Bloat always makes the situation worse.
Second, if a priority transaction goes significantly up in price it will be less suitable for micropayments for services like access to newspaper articles et al, especially in low-cost countries.
Not for Bitcoin the protocol, but Bitcoin as in BTC, the currency, the BTC blockchain etc.
Gold was currency.
Silver was currency.
Copper was currency.
They were in circulation simultaneously. Why didn't they only have gold or silver coins? Because each thing served a different need.
If transactions go up significantly, there is no problem in having spillover of microtransactions into bitcoin-based altcoins. Faster, cheaper and their blockchain is a far less valuable resource that can be ...discarded in the long run if it bloats to unusable levels.
Third, if you get rid of all the "dust" you get rid of a world of opportunities in the internet of things. It's way too early to limit the network in this way,
The protocol exists for all this world of opportunities. People can still use an alternate chain if they want to use the blockchain to store data, contracts, intellectual property etc etc. There is no "necessity" that it must be done on BTC's blockchain. And it won't be some kind of failure if everything doesn't fit in the BTC blockchain.