I too have been looking into super heavies as an addition to my army. I'd not want to bring it every game purely because no one would want to play me anymore: "oh no, here comes the 46th with their rolling castle," but a few of my friends have discussed the potential of playing with one in a themed game. I just got the escalation book and the rules look pretty good, points costs are what I'd expect.
The fact is other than needing many shot and HP removals to take them down, the Baneblade for example has only armour 14 on its front facing, no other, so they're not completely invulnerable. Deepstrike and outflank or encircle it and your odd are more favourable. But it can't be easy to kill, otherwise what's the point?
Never was a big power blob man myself, that said Commies being cheaper and an - I think - improvement to the Summary Execution rule means that even if you do fail an LD test you may not have to shoot your PW wielding Sergeant in the head. However you're now limited in the number you can take: one for every CCS or PCS in your army so the Commie spam isn't as powerful as once was.
Missiles are not my weapon de jour. In fact I just yesterday killed 3 missile launcher teams in order to make them into mortar teams because I literally never used them. Missiles do 2 things - one well (kill light infantry), and one alright (AT). In my opinion if you want to kill infantry directly, Heavy Bolters are where its at; indirectly Mortars are what you want because in the guard its not "hiding" its "strategic positioning." If you want to kill armour Autocannons (Volume) and Lascannons (Power). As for the AA, 25 points for a missile launcher with flakk isn't worth it in my opinion as you can get a Hydra for 5 points less than the 3 upgrades and thats not including the squad's base cost. With the ability to take a Leman Russ squadron as an HQ, losing a heavy Support slot to a Hydra isn't as hurting anymore. A Valkyrie clocks in at 5 points more expensive than the whole squad (base and 3 launchers with flakk) in the new dex but you mention that you're not a fan of planes which I understand. Perhaps my having 2 slants my view a bit in terms of their comparative usefulness.
My struggle personally is deciding which pattern of IG superheavy I would take, I have to do some research but the 40 man capacity Stormlord looks quite tempting.