I'm really torn on this.
On the one hand, a spacefaring civilization capable of launching starships to deep space at warp speeds should logically not be encumbered at the prospect of landing if the need arises. At the very least, a Constitution-class vessel should be able to jettison her saucer section for controlled planetfall. (But this doesn't seem plausible for ships like the Miranda, unless I'm missing something...)
On the other hand, you're talking about landing a starship on a planet (presumably with suitable surface for landing and a habitable biosphere for the crew to exploit), thus exposing the ship, crew and planetary environment to the risk of landing a matter/anti-matter-using spacecraft on its surface. What happens if something goes wrong? What if the ship develops a problem during planetfall or while on the surface? And the ultimate issue: what if U.S.S. Starfire has successfully landed and powered down, then a Klingon, Romulan or other alien hostile ship settles into orbit high above? The hostile ship doesn't have to even come close to scoring any direct hits; just one nuke nearby will ruin everything for the Starfire's crew. There's also the question of what would happen if you had a crew and ship settled on the surface and some natural disaster were to occur (tornado, forest fire, flood, earthquake, meteor strike, you name it). Would a landed starship, in essence, become a "sitting duck"?
The Federation may frown on one of its capital ships being used for that kind of activity. After all, even if the Starship Reliant were capable of landing on a planet surface (maybe she is) fully intact, with the prospect of launching again, there would always be the open question "what if something went wrong?" If the landing were botched, and the Reliant crashed, this scenario suggests the possibility of loosing an entire capital ship, her crew, and whatever cargo she may be carrying. (All this also assumes there is a nice, mild planet to land safely on in the first place.)
Starfleet may also have protocols in place to discourage planetfall. If a given planet is habitable, the Federation is unlikely to want to "take the plunge" into an alien biosphere. One issue that has been mostly glossed over in the STAR TREK Universe is the exposure of the crew to biological agents (a la "The Omega Glory"). It's bad enough if a crew dies because of an alien infection. To immerse the ship in an alien biosphere, risking hazards potentially a hundred-fold greater, would seem out of the question. Then there's the question of the Prime Directive. Forget about why planetfall on many of the inhabited worlds seen in TREK would be out of the question because the presence of a starship would constitute interference with an alien culture. What about the security risk? (Imagine a Connecticut Yankee in King Arthur's Court scenario, only with King Arthur scheming to lead Mongol hordes in the conquest of the prize Starfire.) Even on an uninhabited world, landing could expose the local flora and fauna to unforeseen contamination from the landing starship and crew.
I would expect that the Federation would discourage starship planetfalls in all but carefully planned expeditions. The philosphy that Starfleet would use might be "keep your ship in orbit, even if it's an unpowered, natural orbit on autopilot". If the crew has to leave the ship for a large-complement mission or some forced evacuation, that's what transporters and embarked craft are for. Leaving the ship in orbit means that if anything happens on the surface of the planet, the orbiting Starfire is still untouched. If the Starfire were crippled and unable to leave or call for help, all the more reason to use embarked craft to seek out raw materials for repairs while the ship is partially or entirely powered down.
I would think a more thoughtful scenario would be how the Federation designs and deploys specialized spacecraft for colonization of specialized short-term expeditions.
In one scenario I could envision, a Constitution-class starship would layover at a starbase or other Federation dockyard. The Connie's saucer section would be temporarily jettisoned, kept in storage for the duration of the mission. A specially fabricated one-way-mission saucer would be attached to the Connie, so that the Connie could journey to a distant star with a skeleton crew (possibly the saucer inhabited by a committed expeditionary crew) and jettison the "mission module" for deployment either on the surface of a planetoid/asteroid or to stay in space and serve as a highly protected, highly mobile base. (Like a MASH unit)
Another scenario would be to deploy highly specialized, mission-tailored cargo modules, tugged to a remote mission location by a Ptolemy or
Forbin's Sultana or some robot warptug (
warptugs discussed here). Each transport module would be a near-orbit-capable spacecraft, with the capacity to handle hundreds of expedition/colonization personnel, either to be inserted into orbit to serve as a space station or to be jettisoned into controlled planetfall. These mission modules would serve as either a temporary "base camp" or as colonial "building kits". What these modules would look like, inside or out, is something I can only begin to imagine now.