OK, but the crucial point is how much percentage is your bonus max? The 10% you suggested earlier would, at your rate of gain per minute, mean only about ten minutes difference; hardly worth it. For someone in your position a bonus of 50-100% would be more meaningful.
With that in mind, surely a total rethink of energy would be better. Give all players effectively unlimited energy. The amount you gain per minute would be determined as now, but your skill points would be used to modify that further, say 10 or 20 skill points for an extra 1 or 1% per minute. For game balance there would need to be a maximum somewhere, so maybe any unused energy you have disappears after 12 hours and the refilling begins again.
His complaint is that his bar is full after 75 minutes or so. It's a self-made problem at the end of the day. A bonus based on previous gold spending would be unacceptable. The game is already heavily weighted in spenders' favour (even ignoring the act of spending) without making it more so.