Debating buying adjacent lot, Philadelphia

My wife and I own a rowhome in a high demand residential neighborhood in center city Philadelphia. Bought in 2017 for 260k, now valued 360k+. Mortgage (3.8%) is $1400/mo. We have around 160k equity in the house iirc.

Combined income is around 190k/yr and we're sitting on 190k cash. We contribute to retirement accounts. No other debt.

The empty lot behind our house (used to be a raccoon-filled 3 story shell) was torn down by the city, sold to a developer 2 yrs ago, and is now back up for sale.

They're asking $140k for the empty lot. I'm considering offering 120k. Realtor we trust has confirmed seller will cover fees, we'd pay about $6k total to close.

Pros:

• our back yard (16x16' ish) encroaches into the plot, and we'd likely lose about half of it should the plot be developed. It's to our south, so we'd lose all our sunlight if they slap up a 3 story rowhome. So, defense.

• the lot is substantially deeper than our property so we'd gain a relatively massive backyard for our dog and kids.

• I'd hope this improves the value of our current home. A plot like this that cuts through street to street is rare. If we eventually sold, I'd sell the properties together. Property feels like a safer investment than investing, and better return than parking cash in a high-yield savings account like we have been.

• we could develop the lot someday and rent our current home.

Cons

• 120 - 140k is an insane amount of money for a patch of dirt this small.

Hoping someone with more financial or real estate sense can talk me into or out of this.