for an SQI like that. a upgrade to +4 should not increase the value by more than even 10 k... that's why people just do it. and the problem comes when you want to sell and +0 carded SQI.. the value might actually drop.
sooo.. just do it and sell it. really if you are selling it using 4 elus and i think 2k per upgrade is not such a big deal... but you MUST do it before putting a card in it.