OP said nothing about purchasing anything. Re-read it slowly this time.
Care to explain how one can acquire mechs, chassis, weapons, internals, items, or consumables, without "purchasing" them?
I concluded that the OP was asking if he should buy everything he can while he still can, and with his and his sons playtime on the lighter side, I'm sure he hasn't stockpiled hundreds of thousands of HC that would enable him to purchase all of the missing items, weapons and mechs. Therefore his only option left would to be to purchase things with supplemental MC which completely contradicts your interpretation of the OP's post. So yes, he doesn't actually mention spending real life cash on things, but as I pointed out, he pretty much has to at this point in time due to him not spending hundreds of hours playing the game over the years.
Thats what I really feel he was asking in the first place, whether or not to actually spend real money to have all the cool grandfathered stuff available in the future. Maybe he will interject and clarify what exactly he was asking.
And its really a catch 22, if the grandfathered weapons are overpowered (like many think they will be), then spending money now is worth it, but that is going to severely ruin the game for the new players (and if Reloaded and company can't predict that, then the game already is doomed). If they are not overpowered, then its just about being different and standing out, which is the reason I run an Alpha skin even though its butt ugly.