We have some knowledge of Oumuamua, many inferences, and plenty of unknowns:
1. Oumuamua moved quickly through our inner solar system, zipping past Earth (the planet it came closest to) at an observed velocity that implied an interstellar origin.
2. Working backwards, it's been inferred that Oumuamua entered our solar system from the Local Standard of Rest for our region of the galaxy.
3. It was observed as a pinpoint object -- devoid of any observable out-gassing.
4. Its color has been measured as being reddish.
5. Its brightness varied by a factor of 10, undergoing a regularly repeating pattern that was never observed to change in any significant manner. The latter being one reason for questioning out-gassing as the explanation behind Oumuamua's non-gravitational acceleration.
6. It was observed to move outward, away from the sun, at a somewhat greater speed than can be accounted for by gravitational effects alone.
7. It's been inferred that Oumuamua was in a tumbling motion (inferred from the brightness variations).
8. An early inference (from the light variations) was that Oumuamua might be about 10 times longer in one dimension than it is in another.
9. It's been inferred that Oumuamua is a dense, solid, rocky object, perhaps with some metal in its composition -- inferred from the need for structural integrity if it is indeed tumbling with a 7 to 8 hour period.
10. Out-gassing has been hypothesized to explain the non-gravitational acceleration by some, and ruled out, or questioned, by others
11. Radiation pressure has been hypothesized to explain the non-gravitational acceleration; but for this to be workable, Oumuamua would have to have a density of about 0.001 grams per cubic centimeter -- comparable to the density of air -- which might be difficult to reconcile with #9 above.
So, where are we in explaining the nature of this object? Is it composed of "dark matter"? Is it a lattice structure composed of hydrogen ice? Is it a craft powered by a sail? Is it a discarded, empty shell of some kind -- like a child's giant party balloon, or a thin-skinned, empty fuel tank, cargo container, etc? How much faith should we put in the various inferences that have been made?
Isn't this object unique enough, interesting enough, and with enough scientific potential to justify a mission for a closer look and examination? The old elongated rock scenario seems to be less likely now than something else. Most of those "something else" alternatives would seem, in my opinion, to be justification enough to mount a mission to catch up with Oumuamua for a closer look.