Fine, but if you really want to test some of these you need further data. If you're not getting monthly growth in paid users it could be 1) because your conversion rate has tanked, 2) the number of free users has tanked, 3) the number of first time visitors has tanked, and / or 4) your adwords account ran out of money six weeks ago and you weren't measuring it.
Without that data you can try to "get alarmed and act accordingly" all you want, but you won't have any idea where to start.
Totally agreed that data is needed if you want to act. But the metrics should serve as top-level benchmark which tell if things are going well or aren't. If they aren't, investigating why is the case so can only be done using the data.
Without that data you can try to "get alarmed and act accordingly" all you want, but you won't have any idea where to start.