I'm in Florida where we have many residential pools. I see anywhere from $0.00 to $25,000 for a pool. The $25,000 would be a very large, very ornate, full screen enclosure pool in a subdivision of large high-end estate type houses. Those at the $25,000 level adjustment for that pool probably paid around $50,000 for having it built.
There are statistics appraisers use to make these determinations. Realtors have no clue about running those statistics.
Similar to you looking at a two properties that you are interested in buying, both are identical, side by side, on small acreage parcels - except - one of them has a 3 stall horse barn. You don't have horses, but you think it's a pretty interesting idea to maybe have horses, your children love the idea.
How much extra are you willing to pay for that barn??? After all, it cost $20,000 to build. Then again.... do you really want your children to get into horses? They cost a lot in maintenance and might be dangerous.
Same thinking many buyers have regarding a pool.