I would not recommend buying expensive Beta/Untamed packs unless you are feeling really lucky. They are like expensive lottery tickets.

I don't know what to say about land since it hasn't been implemented. However I also missed out and don't own any land. I have no plans to buy any.

It's difficult for me to give you advice on what cards to buy. Things have gotten so much more complictated. In the old day there were no collection scores or renting out cards or separate rewards pools for editions of cards. Back then buying cards that apppealed to you would have been a strategy that worked.

Here's an example of what I'm talking about. In the old days investing in summoners was great because of their price appreciation. I think today they would still have good price appreciation. However the problem is that they are expensive relative to the collection score they provide and they don't seem to bring in that much money on the rental market. Though, at the end of the day if you are serious about playing, buying lots of summoners should be one of your priorities because they are required for playing leveled up cards that you accumulate over time.

One general strategy many players use is to have one weak splinter that they don't invest much if any money into. Because you have the option of swapping your daily quest once per quest so you never get stuck being forced to use that splinter for a quest. Its also fun to pick a splinter that is your favorite and invest the most money into that splinter.

If I were you I would be prepared to spend money when chaos legion cards flood the market. Hopefully that will also drive down the price of the current rewards cards as well so you can buy lots of those up too.