What do you call a project which is tossed up as a very plump & has potential but is just creating busywork for some people's existence?

You could try using shell, in the following sense:

4c : a casing without substance
// mere effigies and shells of men
— Thomas Carlyle
_{Merriam-Webster}

This metaphor is commonly applied to shell corporations:

11 : a company or corporation that exists without assets or independent operations as a legal entity through which another company or corporation can conduct various dealings
_{Merriam-Webster}

In your example:

The construction job at Crescent Marina was merely a shell [project].

This isn't a single word, but you may be looking at something like a "pork barrel project".

https://en.wikipedia.org/wiki/Pork_barrel

Pork barrel is a metaphor for the appropriation of government spending for localized projects secured solely or primarily to bring money to a representative's district. The usage originated in American English.[1] In election campaigns, the term is used in derogatory fashion to attack opponents.

This can often refer to or imply that monetary kickbacks happened.

Sometimes these projects actually do some good (like when a playground is built), but other times it's just to keep a politicians' friend's (construction) business busy and operating. (I'm not choosing sides, I'm just explaining how I understand it.)

You might also be looking for "make-work". This is a project that makes a department, (school grade) class, or other section of people look busy, while in fact they aren't really doing anything of any real importance.

The military sometimes does this as punishment for lower level enlisted. "Dig a foxhole here. ... Done? Then fill it in. ... Private, are you still going to fall asleep on sentry duty?"

Sometimes this is done by an individual to either avoid real work or to pretend that they are doing something useful during downtime at their job. "I think I'll write an app to keep track of the office supply inventory, even though it only occupies the drawer next to me."

Busywork is a word we used in school to describe work that had limited or no educational value, but we had to do it. I think this would apply here.

make-work TFD

n.

Work of little value assigned or taken on only to keep someone from being idle.

As in:

Many of the suggested jobs seem best described as make-work. Washington Post May 5, 2018

and

This would, of course, create even more government jobs, at a special agency for making make-work. Washington Post Apr 23, 2018