London Pass or Purchase Individual Tickets?

It depends which museums, etc. you hope to go to. Please know that many in London are free to enter, so even though they're listed on the Pass that may be a scam of sorts.

What I always do when evaluating a city's attractions card is to make a list of all the museums I'd like to go to and their entry fees, and whether they are included in the card. Then I just do the math. I'm a heavy museum-goer, so they always work out for me--plus provide the ability to bypass ticket lines and walk straight in.

I love public transportation and enjoy riding cities' subway systems, so I always get an unlimited card. Just like here at home in NYC, I prefer not to worry about whether I need to top up my ticket or buy another when I'm eager to get somewhere. But that's just my preference.

The Oyster Card that you can order with the Pass is not the same as the plain pay-as-you-go Oyster Card that is often recommended here. It is a Visitor's Oyster Card which is set for a fixed amount of time. There are advantages / disadvantages for it. Whether you get the London Pass or not, you can easily buy the regular Oyster Card at the airport or many other locations, and that is worth it.

We looked at getting the Pass for our three day visit and decided against it. After the trip, we agreed that we would not have had time to visit more than a few of the places on the Pass that charged admission.

Dont forget to ask for the concession (senior discount, if it applies to you) if you go for individual admission tickets.

My advice is do not buy the Pass.
Purchase individual tickets.
Museums are free.
Much of London can be enjoyed just by walking around, seeing the sights from the street.
The Pass is too expensive for the use most people will get out of it.

On the top of the list the two sights I would pay to see are:
The Tower of London--walk up to the ticket office and buy tickets.
Westminster Abbey--walk up to the door and pay to enter.

For only three days, you could fill up the rest of your time with museums.

Your question is one which gets asked over and over again here.
Here is a recent thread with lots of answers to your question:
https://community.ricksteves.com/travel-forum/england/london-pass-yes-or-no

What are the things on your own personal "must see" list?

You said, "We won't have a firm itinerary until we arrive
but those attractions we have identified are on the London Pass."

What are those attractions?

Thank you! We, too, have identified the Tower of London, Westminster Abbey, and several museums as 'must see'.

The London Pass advertisements overwhelmed me but now I can clearly see that it's too expensive for the limited time we have.

Yes, we qualify for the concessessions, great tip!

Much appreciate the information.