I don't like being around antennas. Especially when hiking trails take me past one of those microwave horns. Maybe it's a phobia, but I always wonder if hiking trails were taken into account.
Also I don't think any of those are still active, are they? Most of 'em that I've seen have the feed waveguides removed where they get near the ground. I always thought it'd be fun to make an adapter/coupler and stick a wifi card onto one of 'em because 2400Mc is within their passband, but I can't find a pair pointing at each other where both ends still exist.
I used to work in radio spectrum governance, our inspectors who were clambering up towers on the regular made to sure to not stick their head or gonads in front of a focused microwave transmitter for more than 10 - 20 seconds (IIRC).
All of those inspectors have retired now, and none of them have brain or testicular cancer, likewise none of their children had birth defects.
So I think you'll be fine unless you're sticking your head in the dish :)
I measured 20mW/m2 around 2nd and Harrison.
For reference, on a sunny day the sun will dump 200+ W/m² on you in SF.
Q2: How much has ambient RF spectrum intensity risen today vs. natural background levels?
A1: Virtually none.
A2: 10^18