If what you mean by suppressing fire, is firing to keep the heads down of an adversary, I think missiles do that quite well. Any S3 missle will force a foe to fly defensive for a bit and allow you to maneuver behind them. Also note, the only mention we have of spike missiles in game thus far are the Arrester III. If they can knock out a computer, I'd say that's pretty suppressing, and Arresters come with all the Vanguard variants, IIRC.
If when you mention suppressing fire, what you mean is against terrestrial targets (what the Valk is intended for) I think the Sentinel does that better too. If you load up 6 Scorpions, you're shooting 5400 rpm and each round is large enough to end a soldier. If you spot a rover a tiny squeeze on the S4 gimble will end that too, and if you spot a Nova, a single salvo of 4 S3 missiles will make short work of that. If you're on a stealth incursion, and want suppressing fire out to 2 km, you can do that with just the Sentinel turret, while it is on the ground with most systems off. Since the turret is on the top instead of the side, it has a better field of view with the bird on the ground. If you get spotted, then of course you can turn on your shields, and fly the bird, but I think you want to be expert in hover mode for those kinds of engagements.
Also, as per using missiles terrestrially: I think it's is next patch we get the new fps radar builds. If it turns out that personal radar can be fire linked with ships, then it is quite possible you can use the Vanguards as artillery, and call down the thunder. It is possible that you will be able to target a rover, tank or building with your personal radar and fire link to the Vanguard which then fires a missile. That might seem too much to hope for, but it is the kind of thing Chris has talked about in the past, and since missiles are not line of sight, and are used for artillery in the Ballista, it is possible you can use Vanguards in similar fashion. Missiles matter!
What I mean by "It's too high a price to pay until you're in a larger team on a Polaris. . ." is that in order to carry a rover, you have to settle for a slower, easier to hit ship of some sort. If you make a rover a baseline requirement for your bounty hunter ship, that ship cannot hope to fly close to 1kms, and it will be sluggish enough that most other ships will not miss it when shooting at it (which really does matter!). If you want to run your marks to ground, I think you want a Sentinel. If you fly a Sentinel for bouties you can get by on 2-4 players and never need blades nor NPCs. That's a good group for me. If I can find a group with 5 guys that plays 5 nights a week, but most of the guys only make it 2-3 nights a week, a Sentinel means that everyone plays whenever they want. If all 5 guys show then you can field 2 Vanguards and take bigger prizes. Second bird could be a Harbinger if you expect your target in his ship, or a Hoplite if you expect him on the ground, or want to board and take his ship. And lots of folks own Vanguards, so you can team up with other players very easily for large strike misisons, etc. I am looking forward to flying wing with a dozen Vanguard against the pathetic, slimy Vanduul. My their carcasses all rot in the rays of Orion!
Gameplay flexibility and handiness matters. I don't think the Valk will be very user friendly in this way.