Doing nothing is unexcusable...
In your opinion. However others might feel that the status quo is far better than throwing piles of tax dollars at the Allen to bury it, deck it over or fill it in and run a nearly identical road on top.
It is a perfectly running expressway? Of course not. It was intended to deliver cars right smack downtown, but the fact it hasn't laid waste to the Cedarvale ravine or the Annex south of that is a good thing.
The amount of land potentially freed up by any of your proposals (at least what I can decipher them to be) is relatively minor. If there are four lanes and two subway tracks, burying the subway and putting four (or was it five) lanes on top is pretty close to what currently exists. There simply is not the demand for development dollars such that any private money is going to be willing to cover your costs for the public infrastructure.
You said there are already plans for Lawrence Heights redevelopment. The underground LRT on Eglinton has the potential to lure private development money for that street similar to what has occurred on Sheppard from Yonge on east through to Leslie.
There are several parks just east or west of the Allen up to the 401, so unless you want to start knocking down private homes to put in denser condo/apartments, there isn't the really strong need for parkland on any filled-in Allen trench (at least not a need comparable to the cost).
There are far more appropriate things I'd prefer by municipal tax dollars to go towards. Putting in better surface transit routes to deliver passengers more efficiently to the existing subway line would be a good step.