I realize that you're in a somewhat tricky situation, and it seems that you're truly respectful of your spouse and are level-headed enough to view the situation logically. A few observations/questions
To make a long story short, my wife and I are in ungodly amounts of debt due to a couple of majorly bad money decisions that precipitated ongoing small bad decisions because of our refusal to reduce expenses. Today, several years later, we are finally on the right track, paying down what peaked at over $100k of consumer debt and another $85k of student loan debt (today the totals are $77k and $80k respectively). We're also $30k underwater on a $180k mortgage. Don't worry, I have punched myself in the face many times for our sins.
I presume the student loan debt was for her occupation?
Also, in the previous financial life, was your overindulgence approximately equal, or was it always her spending/choices making up about 80%-90% of the reason for the debt growing? If you had just as much 'fun' in running up that debt, then - as other posters have commented - you have to give her some slack in gently nudging her in your fiscal direction.
This year that total will be at least $3k, from which she has already purchased a new laptop and several hundred dollars in designer clothes (the subject of today's conversation). Further twist--she has lost a fair amount of weight over the past few months, making new clothes a literal necessity.
It sounds like she has a 'legitimate' reason for the clothes. Do you think this will be the majority of her clothing purchase for a while, or do you have a feeling it'll be a monthly excursion of retail therapy to help her cope w/ her stressful job? If the former, then remember that many of women's clothes can be expensive. Also, try seeing what types of fashions she likes and/or certain designers. Do you have any stores like TJ Maxx/Marshall's/Ross/etc. that have a variety of clothes (some fashionable), where you could buy her one that she likes and show her how much less it could cost if she buys smartly?
She insists on a nicer car to drive clients around (purchased used, but still $20k)
Well, how long will that $20k used car last? What kind of depreciation per year are you looking at? If you buy a decent used car and the total depreciation/repairs only run a couple hundred/month, it's not that different from buying a cheaper car brand new and taking depreciation hits. Some people could actually argue that buying a used car and wrestling with repair bills (and the inconvenience of running to get a rental car everytime something comes up) could end up being a wash vs buying a modest new car, maintaining it for 8-10 years, and running it in the ground.
and wants 3-4 non-mustachian vacations each year (e.g. Vegas).
Just as with any purchases, there are ways to have a very fulfilling, active life on the cheap.
What kind of budget (cost per day, for example) do you have on these trips? Regardless of where you go anywhere in the world, there are ways to piss the money away like water, and there are ways to enjoy a damn nice lifestyle on the trip for a far less cost. For example, you can get hotels on Hotwire for sometimes less than half of what you would normally pay going to the website. And if you time your trip, you can also get additional discounts or packages.
Right there, you can save 30% of your flight/hotel just by doing a few simple, not very time consuming actions, for not very much change in quality at all! And getting coupons on different shows (if that's what she likes) can likewise stretch the travel dollar farther.
If she's the type that simply buys stuff without researching for the best cost, offer this: tell her to give you some criteria of what her next trip would be like (date ranges, types of hotels to stay at, activities there), and do some research. Come back to her with a list of 3 hotel options, 3 date ranges, and 3-5 activities to do that you found. To get a variety, maybe try picking 1 free activity (like a museum, or walking around town, or a free band/concert), 1-2 lower cost activities, and then 1-2 higher price activities (but with a Buy-1-get-1-free/Groupon/other coupon)....but don't tell her any prices. Then after she picks, ask her what she would pay for a trip like that. Subtract the actual cost of the trip, and then tell her that you can put the savings towards paying off additional debt.
When I retire, I'll be enjoying quite a bit of traveling with the future Mrs. MooreBonds. Will we be spending a fair amount overall? Sure. But our cost/trip will be pretty good, given my scouring to get the best deals, and purchasing in a smart manner. So you can still live on a modest budget with tons of fun along the way.