Whether your frequency of payments is a few dollars every month or a few hundred dollars every few years, you're still investing money over time in software. It really comes down to how often you want those payments to be, and how much you want them to be.
In your case, you might spend $140 every 5 years. That's probably on the extreme low end, but certainly not unreasonable. It's equivalent to putting a couple bucks every month towards your software. If Lightroom was offered on a subscription for $2/month, you'd be just as well off either way (probably better because you'd be getting the benefits of access to the latest release over that period).
We don't know what the monthly cost of Adobe Lightroom is, because it's bundled with Photoshop, but we do know that keeping current with a perpetual license costs $140 initially plus $99 every couple of years for what amounts to the equivalent of $5-$6/month (over 5+ years). Now, if you value Photoshop as much as Lightroom, their $10/month plan is a good deal. If not, then it's not a good deal.