this is true, but don't know if I will ever find the limits of the bike but I have upgraded most if not all components on my bikes that I did not build from the frame up.
True. So if you are not finding the limits of the bike then upgrades become an more ancillary part of the bike vs. a necessity.
In this case;
Necessity would potentially equal finding the limits of your bike, breaking a major component, outgrowing said bike, or parts availability necessitating a change (e.g. parts no longer available or cost of said parts is restrictive).
Outside of that, the ancillary part is where you are replacing more out of maintenance/wear and tear than anything else. In that case, the shock is dying and thus needs to be replaced however the same brand/model is no longer available or has been upgraded. Again this become more part of the maintenance and upkeep of the bike.
Most importantly, get whatever your max budget can afford as that "should" hopefully get you out on the trails more and allow you to be more "current" with the trends. Robert (B1KER B1) just talked about this in a recent garage talk about where just because you are getting a hardtail does not mean that it is any less of a bike than a full suspension. You
can still have tons of fun on a hardtail vs. full suspension and it will teach you different skill sets. Sometimes new riders associate getting a hardtail with getting a
cheap bike, when in all actuality it is still a phenomenal bike for what they are doing. This is why I say, get whatever your max budget can afford, if that is a higher spec'd hardtail vs. a lower spec'd fs, then you are doing better with the higher spec'd hardtail in the long run. Why? because those parts have the potentially to be shifted to a fs frame later down the road if you so desire.
To many times you see new riders looking at bike purchases as just a
thing instead of looking at it as an investment. If you invest properly, you can potentially continue to move that investment from one bike to the next, to the next and so on (depending on timeframe between).
With that, for the OPs two different bikes (07 FSR vs. 15 Scale) I would personally go with the Scale to get a better, more current frame/geometry. Swap the parts from the old bike that will fit and upgrade those parts as needed. The full FSR will potentially be more time consumptive and costly simply because of the fact that it is a much older bike.
