We are hoping to go to Ko olina in 2024 and my husband is worried that our NCV won't be able to trade for it in II (because of the sales pitch where they said marriott is pulling all their inventory from II from now on). We were offered to be able to enroll our deeded week (that we bought on redweek in 2020) which we were told we would NEVER be able to enroll- but we'd have to buy 2500 additional points (so with the points our week would give us we'd have 5975 points when we don't elect to use our week as a week on it's own).
I personally think it would be better to buy a second week at NCV and just trade it or sell it.
I can't comment much on II because we don't use it much for trades, but from what I read here, Ko Olina is not a hard trade.
I own at NCV both enrolled and unenrolled weeks. I'll give you the following perspective. The 3475 points NCV Platinum converts to are a low number relative to the real value of the week. What I mean by "real value" is rental value. For example, if you are part of the DC Exchange you can rent 3475 points from another owner for about $2400 (assuming $0.70/point rental cost). But your NCV Platinum reservation will rent out for $3500+ (if peak summer week). So if you want to use points in a given year, a good strategy would be to book a summer week, rent it out and then use that cash to rent 5000+ points, which is 50% more currency than 3475. Of course to rent points you need to be a part of the DC exchange, which you can do by buying 1500 (maybe as low as 1000) points resale which should cost you about $6/point. Then you can rent more points from others as you need them.
I clearly like your idea of buying a second NCV week better, since I own several myself. If you own 2 weeks you will be able to make reservations at 13 months out and increase your chances of getting the reservations you want. Moreover, and this is important to keep in mind, if you ever decide to enroll your weeks in the future, odds are that the cost of enrolling 2 weeks will be not much higher than you were offered for the one week, so you get a better "bang for your buck" enrolling multiple weeks and you will also get to Executive status (7000+ points) which is where the greatest jump in benefits is.
Frankly, it's nice to have weeks enrolled and you feel like it adds flexibility, but the only NCV weeks worth considering trading for DC points are the Platinum Plus week 26 and, to a lesser extent, Platinum Plus week 52 which convert to 5300 DC points and 4625 DC points, respectively. Otherwise, the rental value you'd be foregoing by trading for points is too high for just 3475 points, and those 3475 points often don't get you as much as you'd like.
We have always been told we couldn't enroll a week purchased outside marriott - and yesterday they said this is the only time we'd be allow to enroll our external week. Is that not the case?
If we were to buy an Aruba week how would we enroll it?
These offers have always been around, and you will likely always get them in one form or another. It's their best method to entice resale buyers like you to buy from the developer... If you'd consider paying a large sum to enroll resale weeks, my advice is that you should attend a presentation with as many resale weeks in your back pocket as you can have, and don't take the first offer.
I personally suspect the cost of enrolling weeks will go down significantly over the next few years, as it did on the Vistana side. Vistana used to require $20K purchase to "requalify" a week and $40K if that week was in the Hawaii or Caribbean. Now the requirement is $10K for 1 week (any week) and $5K for additional weeks. There are only so many people willing to pay $25K-$30K to enroll a week into an exchange company - then prices have to come down or their closing rates (a metric they disclose in earnings calls) will tank.