Am I freeloading at my LBS? I try to make all my bicycle-related purchases (parts, tools, accessories, etc) at my LBS, but I have never bought a new bike at a LBS, and I (very) rarely take my bikes in for service. On average, I probably spend $30 month at the shop, and I only buy stuff half the time I come in.
In the past, I've always tried to build up a good relationship with the folks who work at the shop, because I often come in to ask questions and just talk about bikes.

My question is: am I freeloading, or am I a (financially) valued customer?

For the record, they have always been helpful, and have never given me the impression that I was unwelcome. BUT, when I come and ask about - for example - putting disk brakes on a 90's Hardrock frame, they will suggest that it will be easier to just get a new bike.

The root question might be: what are the typical profit margins on new bikes, repairs, and parts?
I know for a fact that I could get parts significantly cheaper on Amazon, but like I said, it's nice to bounce ideas off LBS mechanics in-person.

Note: I am talking about both small privately owned shops, and larger chains (eg, Performance Bikes), over a period of multiple years.
Spending $30 / month at your LBS seems perfectly reasonable. Your LBS is grateful you buy from them instead of from Amazon.

If you sometimes go to your bike store just to talk, that probably OK, as long as you are not distracting any staff from real work or keeping them from serving customers who are paying. Either they actually like chatting with you or are willing to humor you to keep your $30 /month, possible larger custom in the future and to maintain their reputation as a friendly, helpful store.

The example you gave about putting disk brakes on a 90's Hardrock frame - yeah, they were absolutely correct about that! They were not just trying to sell you a new bike.