I was thinking we could post some ideas on levelling up faster or collecting gold.
When a new box appears in the hub (for increasing your portal master rank), always stand beside it and not under it, so when it is opened you do not automatically collect it if it is gold or a ball (which gives you a one level increase). Put in a high level skylander to grab the level up. For example, one of my Drobots was level 16. I used the level up for him to save some time - don't use it for a low level skylander that you could quickly level up anyway through a moderate amount of gameplay.
When playing Kaos' Doom Challenges, after a wave is complete (but before you collect any gold or experience) put in a low level skylander to give a quick experience boost when you start the next wave, or put in one that you are wanting to upgrade -especially after a series of waves is complete when the area is covered with money and a treasure chest is there to be opened. All gold is automatically collected when the next wave is started (so it is easy to pop in a character for the gold and exp, then switch them back out to whichever character you are playing the waves with).
I think Skylander Dad came up with this basic plan. The Sky Diamond now is short and gives you money only for breakin destructible objects - so use it when you have an area filled with them (such as the start of an arena or Kaos challenge), then use a skylander with a long range attack to break a lot of objects before the diamond runs out. The Piggy Bank gives you increased coins from killing enemies or using after a wave of the Kaos challenges is done (his suggestion was to use it after your towers were level three). Remember you can pull the Piggy Bank off the portal andput it back on at the end of the next round (to make it last longer).