The tangible reward is getting paid a good wage. Honestly under socialism we should probably compensate the crap jobs way better than the by-comparison comfortable jobs. I know how horrific and exploitative even small businesses can be. Increasing the wage and giving those workers rights and leverage is a good way to start, and if a kitchen can't pull in workers to do its crap job, good riddance.
Welcome to post-industrial capitalism, the age of grift, where this happens all the time and billions of dollars are wasted or stolen in the name of "innovation" and "technological progress!"
This is just shooting in the dark. There's no reason to assume this stuff can't be done under socialism. In fact we know for certain that socialist economies can develop proficiencies in, for example as you say, manufacturing and engineering.
Like you say who pays for 10,000 failing restaurants - I ask you, who really does pay for them? Under capitalism, when enough small businesses fail and enough loans default, the markets crash and *millions* lose their jobs and livelihoods. Many restaurants are opened with loans that will never be paid back, with a few greedy individuals making big money off of others' failure. The crashed markets are then bailed out by monopolists who pay themselves for being too big to fail. Under socialism, credit could be far more transparent, far fairer, far less indulging in the disbursement of MASSIVE loans that can never be paid back, and so on. Predatory lending replaced with socialist lending.
The dirty secret of capitalism is that this "growth" that exploitation achieves, growth you are anxious about now occurring under socialism, is mostly a lie. It is not "growth" of the economy, it is profits for a select few. There is a correlation there but that is not the same as saying those profits are necessary for growth. Actual growth is a matter of the physical work that people are doing, the goods and services they produce. When the population grows, and the growing population starts working, of course the economy starts growing as well. Why would people work? Because everyone would work.* Exactly the opposite of capitalism, where some people never need to work and live off of welfare skimmed from the working class.
Who needs exports? Export what you can. Make what you need. Under socialism I expect people would work a lot less and more environmentally conservative services would take up the bigger portion of the economy. Things like going to movies and getting your hair cut, which don't really require any additional input beyond labor. People would have less stress and be better positioned to enjoy the leisures of industrial society. If we're not shoveling some broken kitschy publicity stunt water pumps on African economies, so much the better.
I mean all of these nagging little details are really missing the forest for the trees. The point is there's no reason to expect that a socialist planned economy can't conduct the same basic maintenance of society objectives that capitalism can. Your mobile phone can still be designed and produced, albeit in a far less exploitative fashion and burning far less capital lining the pockets of executives who don't do anything anyway. What is a supply chain? Someone needs something, they order it from a distributor, the distributor distributes it. Why can't that be done with socialist businesses? There is no reason.
* Accounting for disabilities and people with special needs and conditions, of course, because we aren't barbarians and caring for the most vulnerable members of society ought to be a basic objective of human decency.