The concept is good, and great advice for most, but...
I have an underdeck fuel tank, and the only place the fuel line is accessible is at the filter (I repplaced the mounting bracket, and it's just barely accessible there, from experience) and the jump between the transom and the outboard. A spare fuel line would be a waste of space, as I doubt I could replace it on my own sitting on the trailer with my garage tools handy.
Definitely avoid Tempo, unless you can do a thorough check of the part before purchase. The Tempo bulb I bought wouldn't even pump air, much less fuel (squeeze the bulb, and that was it until it decided to reinflate an hour later.) In addition, every fitting that had been designed for my tank and motor had to be slightly modified to fit, lock, or not leak.
A fuel bulb that doesn't stiffen up can be caused by a few things: a leak past the bulb (motor side), incomplete sealing on the intake of the bulb, just to name two.