What if the speed of light really is ultimate? What if radiation really does decrease by the inverse power law? What if it really does take all the energy and time to cross the gulfs of space that we think it does? I read a paper once that pointed out that "interstellar hydrogen" is a guess, not a fact. What we think of as the interstellar medium may end at the Oort Cloud. At that point, all your beautiful dreams of Bussard ramjets and VASIMR flame out and leave you in the deep black. Ockham's Razor on extraterrestrial contact is it's more trouble than it's worth.
I think the speed of light really is ultimate and that it would take a Kardashev III+ civilization to make long distance space travel feasible. At that level of energy expenditure, you’re not flitting around the ‘verse and chatting it up with whatever local yokels you happen across. Interstellar hydrogen is probably there but maybe not at any kind of concentration that could be used for propulsion.