The quantified costs are:
2. Lack of skill variety during play
3. Lack of item variety during play (assuming appropriate items have not been reserved)
4. Time consumption to achieve previous level (not to be confused with desired level)
As time consumption is the only cost being sought preservation, a possible solution would be a time scaling mechanism integrated to proportionately adjust for the time consumption desired by the player. While a casual player may desire to complete a character in 6-8 months, a dedicated player may desire to prolong character completion -thereby extending entertainment value-, possibly to a length of 5-7 years.
As End Game activities are arbitrarily precluded as a benefit to the dedicated gamer cohort, it is conceivable that some may desire to scale completion time to the limit of infinity.
If more immediate costs are desired, you could always shoot yourself in the foot whenever you alter your character, thus improving you cost/benefit ratio.