FWIW. My impressions on frames/forks may differ from that which other people have ... to simplify:
- My impression is that frame GEOMETRY has a greater impact on how a bike rides than the material it is made with -- head tube angle & (secondarily) wheelbase.
- beyond aesthetics, the only benefit in going to a CARBON FIBER fork from a good STEEL fork is a weight reduction ... the drawback is that 700x25 is usually the largest tire size which most CF forks can accommodate
- There is SOME benefit in changing an aluminum ALLOY fork to a CF fork.
When in doubt, use a 700x25 tire instead of a 700x23-or-smaller tire ...
If they will fit in the Klein frame-and-fork, 700x28 tires at 90-to-95 PSI will give you the boulevard ride you are may be looking for.
The ONLY drawback to the bike's drivetrain is the 8-speed cassette which it will have because the cogs will NOT be ramped ... ramping cogs didn't begin until about 1998 ... ramped cogs make up for any-if-not-all of the sins which may exist in the indexing's adjustment.
IMO, a real benefit is that you will be introduced to Campagnolo's vastly superior ErgoPower shifters (when compared to Shimano's STI shifters).
An 8-speed Shimano-compatible "wheel" can be used with 8-speed Campagnolo shifters & derailleurs ... that is, AS LONG AS you adjust the stops, accordingly, because the cog offset from the centerline will be slightly different ... you may-or-may-not need to subsequently adjust the indexing.
- FYI. You can even (!?!) use a wheel with a 9-speed Shimano-compatible cassette with the proviso that you understand that only 8 of the cogs will be found by the shifter's indexing AS LONG AS you are using a 9-speed Shimano chain (or, equivalent).
A CF seatpost will provide almost zero benefit, BTW, with regard to the how the bike feels ... it may-or-may-not be lighter than an alloy seatpost ... IMO, the greatest benefit of a CF seatpost would be if it satisfies your aesthetic sensibilities.
BTW. I suppose that one of the reasons which early aluminum frames received their reputation for having a harsh ride may be attributable to the earliest Cannondales ... one of the reasons why Klein frames were so highly regarded was because the ride was not considered to be harsh ...
While my preference is for a steel framed bike, that is as much an aesthetic choice as a practical one ... and, I have a pretty nice CF bike ...
If you were really motivated, you could probably tune the ride of the Klein to mimic-or-almost-so the ride of your Masi ([COLOR= #808080]unless you have a 60s vintage Masi, I'm presuming that both have 73º head tube angles & approximately the same wheelbase[/COLOR]).
Regardless, if I lived in your neighborhood I would be knocking no your neighbor's door with a-fistful-of-dollars for here ex-husband's Klein!