Martinez is due $35 million over the next two seasons. Good luck to Moz trying to find someone dumb enough to take that contract without having to throw in a couple of younger players who actually have value.
Ditto with Carpenter, who is owed $37 million over two years. 
Fowler has one year left at $16.5 million. He might be a guy the Cardinals can move at the trade deadline if they're not in contention for a playoff spot.
They owe Goldschmidt $100 million over the next four years. He's going nowhere. 
You might be right about Wong. But I still like his defense. 
It's hard to judge the young guys by what they did this year because the season was so abnormal. O'Neill has another year of team control. He'll be back, but I don't think he warrants 500 at bats. I'm more worried about Bader. If he could just hit .250 instead of .220, I'd keep him around for his defense.
I see no reason not to bring Wainwright or Molina back.

Pitching.

Dump Martinez. I’m not sure how much value he has, but I think he’s a case of addition by subtraction. He’s a distraction and he’s not good enough to be worth the headache.

Supposedly Milolas will be back. Re-sign Wainwright. Flaherty and Kim give you 4 starters and let Ponce de Leon and Gomber compete for the 5th spot. It’s not great, but it’s not terrible.

I assume Hicks will be healthy and ready to close. If this season provided any value, they got to see a lot of people. They should be able to cobble together a decent enough bullpen with what they have. 

Short version, this off-season should be devoted to upgrading the offense.

I understand what you're saying, but sometimes players will thrive if you put them in the right position to do so.  IMO, this is one of the things the Cardinals have been really bad about, especially since TLR left.  

For example, it's probably unrealistic to expect Paul Dejong to ever be a very good #4 hitter.  But I still think it's possible he could be an effective hitter and a piece of a pretty decent lineup if he was hitting #6 or #7 instead of #4.

I haven't looked at potential free agents, so I have no idea if the market even offers what the Cardinals might need to fix this mess.  But it's pretty clear they need at least one guy who can hit #1 or #2 who can get on base in front of Goldschmidt and a legitimate #4 hitter behind him to provide some protection.

I've bitched all season about the decision to let Ozuna walk.  To be clear, I wouldn't have given Ozuna the long term deal he wanted when he hit free agency.  He came to camp out of shape and clearly hadn't done his rehab as the team wanted, and I get that might have left a bad taste for some.  But when the market didn't materialize, and it became apparent he was only getting a one, maybe two year deal, there isn't any reason the team shouldn't have re-entered the bidding.  Maybe they did, and maybe by that point Ozuna was pissed off and wouldn't come back.  I don't know, although I recall some stories around that time suggesting that wasn't the case.  The Cardinals very confidently proclaimed that the variety pack of outfielders they had would replace Ozuna's production.  They didn't come remotely close.  

Again, just my opinion, I don't think they make wholesale changes.  I suspect they'll bring in one new body (but not a premiere name) and you'll see some combination of Carpenter, Fowler, O'Neill and Bader flailing at pitches again next season.  Fact is, they made the playoffs again, and I suspect the front office will try to tell us they don't need a major upgrade.  Anyone who watches (and admittedly, I rarely watched) can see they need a lot of help, but until they completely implode, I don't think it will happen.

The problem with tanking is that it implies an ability to evaluate talent.  Just because a team consistently drafts near the top doesn't guarantee future success.  The Cardinals have shown me very little in the way of an ability to analyze or develop talent.

Without trying to hard 21 free agency list

3b
Justin Turner
Todd Frazier

Of
Brett garden
Ozuna
Joc Peterson
Starling Marte
George Springer

I suppose you could create a meaningful addition to the team out of that group.

Here's an article with the top 25 free agents, along with some notable players with options and opt-outs

https://www.mlb.com/news/mlb-top-free-agents-2021-class 

"The Cardinals rank 23rd of 30 teams in home runs since the start of the 2017 season, and their 51 homers in 2020 was a league low.  There’s no easy way to correct this power shortage, leaving The Athletic’s Mark Saxon to speculate that St. Louis might need to make some tough choices to get some more pop into the lineup without drastically (or at all) increasing payroll.  For instance, could the Cards again trade from their depth of pitching prospects for a bat, even while their need for additional arms might be greater in 2021?  Or, a more drastic option could be to decline Kolten Wong‘s $12.5MM option for 2021 and install Tommy Edman at second base, freeing up some money to land a slugger."

Arozarena might look good in a Cardinals uniform right now.

Liberatore better be really good.

A year ago, we probably would have said there’s no way O’Neill could be worse than Fowler. But he was. And yeah, as much as I despise Matt Carpenter (and I do despise Matt Carpenter), there are plenty of guys in the minors who would post worse numbers in the major leagues.