Honestly I don't have much to share that hasn't been stately already but here are my thoughts to share:
It is definitely a worthwhile consideration and the OP is smart to include it and all foreseeable operating costs in decision making. Transient rates vary much like hotel rates, higher priced areas will have higher priced rates and marinas with more amenities tend to charge more. The value of a pool on a hot summer day and convenient laundry facilities is worth considering. Another consideration is how much you value air conditioning, if you need to run the generator to cool down the boat for more than a couple hours in order to sleep, the operating costs of the generator are pertinent. There is a interesting thread on this discussion alone (personally, I think most generators fail due to lack of use versus overuse).
If you do enjoy anchoring out, the availability of a dinghy dock is very useful information.
As others have mentioned, the LOA is a more practical measurement for transient slips, largely due to logistical reasons. The dockmaster is frequently balancing efficient use of dock space with providing everyone adequate room to maneuver. This is especially challenging during peak seasons and weekends. Docks are generally organized by slip length and are grouped in about 5' increments so if your 34' boat has a 2' swim platform and 2' bow pulpit, they will want to put you in at least a 40' slip to avoid your boat sticking out into the fairway where it is more likely to be hit by another boat or inconvenience another boater.
Many marinas (especially larger ones) have dedicated transient docks or bulkheads which is more straightforward for them to run because the dockhands aren't running all over the marina to assist tie ups and welcome transients. This also reduces the probability of transients hitting a slip holders boat which is a nightmare the marina wishes to avoid. At smaller marinas or during peak demand a transient is more likely to be assigned a slip among the annual slip holders and when these boats are an inconvenience to the slip holders due to poor docking, the marina management is going to receive complaints.
The value of swim platforms and bow pulpits will vary boater to boater. An ample pulpit can reduce the risk of beating up your hull with the anchor when launching or retrieving it, if you rarely anchor this will obviously be less important to you, but if you primarily anchor you are less concerned with minimizing LOA. On some boats the swim platform is used to carry a dinghy or is the best place to board and handle dock lines. If you are a liveaboard that rarely leaves the slip a swim platform is much less useful and could even be removed. There are a few boats that really maximize the living space for a given length overall and while it is a niche market, they have a loyal following of cruisers. The Kadey Krogen 36 Manatee and Great Harbor GH series are good examples of maximizing living space.
The decision should vary on a number of factors and therefor you will likely find yourself splitting your time up between anchoring and taking a slip. I enjoy swimming off of the boat (when there are no jellyfish) and exploring in the dinghy, I also sleep just fine at anchor so I enjoy anchoring more often than not. However, I also enjoy shooting the breeze with other boaters (hence using this forum) and learning from their travels which is a benefit of taking a slip. A regular slip with pilings to keep the boat off of the dock is my preference over being tied along a bulkhead and I enjoy gaining experience docking but many cruisers (and nervous dock hands) would just assume have the convenience of a side tie up where all of the transients are together. Just like every boat, every option is a tradeoff.
