I wouldn't buy extra 8-speed shifters. If/when the current ones die - that's the time to upgrade to 10-speed. An extra cassette or two and several chains make a lot of sense, though. Those wear much quicker.
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"The older you do get, the more rules they're gonna try to get you to follow. You just gotta keep livin', man, L-I-V-I-N." - Wooderson
'14 carbon Synapse - '12 CAAD 10 5 - '99 Gary Fisher Big Sur