I've heard this related in the context of seven-figure businesses with ginormous ad budgets, but it seems to hold true for us wee folk as well: there is an unexpected lift, even across platforms, from more spending on one campaign. A rising tide and all that.
Facebook spending for us has been a rocky path but we are slowly getting better at our marketing and products and becoming a little less risk-averse. It's hard to spend $1000/day when things are so inconsistent and you aren't making enough to cover it in your business: that's an awful lot of risk.
Our most recent campaign - a four week run up to a 3-day live event online - has been relatively consistent so we are back to spending around $500/day. I've noticed between the extra spend as well as the addition of the optimization in the ad to add 'site links' over top of the creative has resulted in purchases of other products that we were not expecting. People either buy the core offer and also see and buy something from the store, or they can't afford the core offer but are still interested enough to buy something less expensive.
I believe that there is an amount of spend that you have to reach to get this lift. Maybe at $400/day or more for us at least. That's not very encouraging for most small businesses who do not have that kind of cash around.