"When is buying boots worthwhile? Buying skis? Is going on a ski vacation to a destination resort as a beginner worth the time and money?"
As someone fairly new to skiing though I've visited some of the best ski areas in the Western US and yes I did put on skis but can't say I actually skied.
I offer the following (Much of which is already mentioned but worth repeating):
Hopefully you are in an area that offers nearby skiing though a trip to a resort can offer a lot of learning in a condensed package that does well for a newbie.
1. If you go to a ski area or resort with friends who are skiers, wish them a good skiing day as they head for the lift and you seek out beginner classes. Don't expect your skiing friends to be the ones to teach you. Friends who ski typically aren't instructors and too often an experienced skier will take a friend up the llift for some instruction... then the friend skis away leaving you to fall your way to the bottom of the hill and you (hopefully intact) make your way to the lodge/bar to grumble and spend the remainder of the trip wonder why you're at a ski resort.
2. After a Class, take what you've managed to absorb to the bunny hill for as many repeat runs as you can manage.
3. If you can manage it timewise, arrange for two to three daily 1-2 hour lessons in as close a rime frame as you can.
4. If, after two to three days of instruction and practice you find you are starting to have fun, plan a few day or weekend trips to your nearest ski hill and play/practice on the green trails.
5. By now you're either hating it or really starting to have fun. If you're truly hating it, take a trip to th enordic center and see if you're more the slow and scenic type. Nordic skiing has its own charm and is fantastic exercise.
6. If you're liking Alpine skiing and your budget allows, this might be a good time to look into a ski boot purchase or if you're really hooked (I was) go for a package. Make sure your boots are fitted well. Boots make a huge difference in learning and advancing. Skis matter too but you may find you're outgrowing a novice ski midway into your first season so might be better to wait and use rentals for a bit. I was lucky and my first skis were and are perfect for my intermediate level, wife replaced hers after a couple of months 'casue they were not enough ski for our home mountains (wouldn't float on PNW Cascade Concrete, just sunk in and bogged down).
7. Go on a Ski Vacation or to a resort? What better place to ski/learn to ski? I don't know of ski area or resort that doesn't offer instruction and maintains a staff of qualified instructors and has beginner's hill and at least a couple of easy runs. At a Resort or ski destination vacation you don't have a drive to or from the mountain and can spend the off time just enjoying having some off time!
My wife and I had spent most of our early life in warmer and snow free climates. Now after relocating we're lucky and live a bit over an hour from two ski areas.
For me and my bride,it was cross country skiing to start. After the many bad experiences at Alpine Resorts I was done with downhill... or so I thought. I was coerced by the pretty one to visit the Nordic Center at a nearby ski area and at age 60 actually took a skiing lesson (classic nordic), it was fun and got me off the couch during the winter in the great Pacific NW. At the end of our third year of nordic trails we ran out of snow at the lower altitudes and I suggested we go to the mountain for one last visit and take a downhill lesson. I guess three years of sliding around on the skinny skis and the accompanying falls (my tried and true method of slowing down when going faster down a hill than I cared for) at least gave us a sample of skiing and I at least understood the snowplow (wedge/pizza). The downhill lesson was fun, we skied the bunny hill for hours and couldn't wait to go back.. but of course it was the last day of the season.
Next season, first snow we somehow ended up at the nearby sporting center and amazingly came home with Downhill skis, boots an poles. The following weekend we were back at the mountain to see if we remembered anything from the previous season's single lesson... we did, in fact after three more practice trips we signed up for a series of lessons and added season passes. At age 64 I was a fledgling Alpine Downhill skier. A year later we've both skiing the Blues working on our carving skills and having a blast! We're not expecting to ever be racers and probably won't ever be skiing a a Double Diamond run but we are skiing and loving it.
No matter about age, just go do it!