Lifelong Serial Founder/PM here. The one biggest thing I see missing from most comments (which in general are quite good) is that the role of the PM and the decision framework depends very highly on the stage that your company is in. Are you pre product/market fit? Are you just seeing traction? Are you in hyper growth? This should massively change your decisions.

There are endless frameworks for balancing these choices. For me, they all come down to this:

Value

1. Dollar value; in either revenue unlocked or money saved (and money can be customer support time)

2. Strategic alignment; how is the item aligned with overall vision & goals? If this item is completed, does it make us stronger or dilute our value / competitiveness? This is really where stage of company comes into play.

...vs...

Cost:

1. Time; Estimated time to build/support. This can be a wag from the engineering team.

2. Risk; what is the uncertainty around the time and maintenance estimates?

Using a framework like this allows you to include architecture, technical debt maintenance, etc into your overall planning and decision process. This will help make visible to business stakeholders the true complexity of operating the product and hopefully lead to better PM decisions. Everything is a trade-off.

Remember: one of the most important jobs of a PM is to say NO. You are the process gatekeeper to how the company spends a ton of resources.

Happy to discuss further.