Ideally, as many nodes as possible is the main goal.
This is not a constructive or engineering approach. Any system has optimal parameter values, or an optimal range. An unlimited increase in a parameter is usually never required, and often leads to unnecessary costs, and the effect of the increase is close to zero.
Therefore, it is more correct to set the goal in a different way: for Bitcoin to work reliably, the number of full nodes should not be less than a minimum level of N. Next, we need to find out the value of N, and ensure that the number of full nodes does not decrease below this level.
Now we have ~10 thousand full nodes. It may well turn out that this is already above the minimum level and further increase does not give any profit for the entire system.
You think that the number of full nodes should be increased. You could use the numbers to show what will improve in the system, and how much.
Once we are able to define reasonable metrics for the merit of full nodes, they can serve as a basis not only for a more rational discussion about amounts of full nodes, but also for an incentivizaton scheme.