Crankarms like omniums/75s/DAs will be of higher quality and in turn have increased functional/performance qualities (stiffness/weight/etc). Though others may use aesthetic/vanity value alone as reason to "upgrade", oohing and ahhing at their newly acquired Nitto/Thomson/DA part as their perceived street cred increases.

It is up to your opinion to determine if the "upgrade" is worth while. You can be perfectly satisfied with your Kalloy seatpost and feel that a Thomson post is not necessary.