[Scarlet Spear / Sentients / Boosters]

Resource Boosters/ Drop Boosters only affect resource type item, they have no effect on items, parts, bps, or anything of that nature.

 

Warframe abilities like Ivara's Pickpocket, Khora/Atlas/Hydroid's augments, or Nekros's Despoil are the only way to increase item/part drop chances because the force an extra roll on the loot table.

[Has the value of prime frames gone down, or have people gotten cheap?]

All of what has been said but especially wanna echo the Riven Problem.  They're a huge plat black hole for the whole economy and because of how ridiculous the grind around them is people with plat wanna dump top dollar on that rather than a slightly better version of a frame.  The longer rivens are in the game without a more reliable, less taxing way to farm/roll them the cheaper everything else is gonna get.

 

This is especially bad on consoles where we only get 1 or 2 plat sales a year, most benefitting the top bundles.  Hell, PS4 didn't even get a Holiday sale around Christmas this time.  PC meanwhile gets plat coupons in place of market coupons making the currency flow a bit more regular.