Not sure if you're religious or not. If you are pray about it first.

So here's my opinion:
I would say since you have communicated the need for a tablet with your wife, and have looked at the financials, if she's ok with it, then you should go ahead and buy it.

Some of the most weathly people started out/or were in a similar situation like you at some point. The road block 99.9% of the time is going to be financial. However, if you truly believe that your skills are progressing as an artist and buying this tablet will help take you to the next level, then it's completely worth the risk! You mentioned that you aren't quite 40 yet. This is perfect, because you're still young enough to where even if you loose on this investment (I'm almost certain you won't), then you'll have plenty of years to make up for it!

I know some people might mention you need to take care of things by a list of prioritizing. Although I do agree that the tablet is on the lower list of priorities right now, I do believe that in the long run, if taken seriously, your ROI I'll more then pay for the tablet, and help pay for other necessary items as well.

I hope this helps, and God Bless!