I often service watches that are worth less than the cost of the service. These are usually family heirlooms, but not always. Some people just like to look after their things properly in order to make them last. You seem to like the watch and have no intentions of selling it, and you will be wearing it a fair amount, so for me there would be no question but to give it a proper service.
Servicing a cheaper movement doesn't take less time that servicing an expensive movement, in fact to get good results it often takes longer. So labour really isn't going to be cheaper for a cheaper watch, unless corners are being cut.
When I'm asked to give advice about this question of servicing or not, there's no one size fits all answer. In this case I would consider the things you already have, but I would also mention that you should think about the pricing and availability of replacement parts. If this was an ETA 2824-2, I would likely give very different advice than for this vintage Zenith Cal. 40. First, since this is a vintage movement, how many parts are out there and are they still being made? I can't answer that but my guess on the second part is no, they are not being made any longer.
Looking at Jules Borel for some quick prices, the Cal. 40 parts are not over the moon expensive, but they are significantly more than say the 2824-2 parts. Some quick comparisons show that a new third wheel for the Cal. 40 would be $32.22 US, where I pay $7 Canadian for one for a 2824-2. A winding pinion for the Zenith is listed at $36.05 US, and I pay just over $5 for one for the 2824-2. Most parts have this sort of price discrepancy between the two movements...
So I would just encourage you to consider that not servicing it, if you intend to keep it and have it serviced at some later date, may be a bit of a false economy. Of course parts could already need replacing now, so who knows without actually getting it fully apart, cleaning everything, and inspecting it all under a microscope.
Just a few things to consider.
Cheers, Al