IMO, watches are not worthwhile investment. Just like cars, one buy a car at RM XXX price but after some time the value drops like "a bird without wings".
Some watches may have certain value as the year goes by, especially Roleks. This, IMO, is because the company increases its prices every year, hence the pre-owned market also adapt to the situation.
Coming back to your question, is it worthwhile to get the Explorer II? IMO, if the watch "sings to you", ie you feel like "must have" that Explorer II )within your budget), then why not get it.
As for trading in your white gold oyster date, does this piece still has a place in yoour heart? If it does, keep it. If not, sell it or trade it for another watch that you feel like "must have".
(Note: I do not discuss price here, as to me the prices can be compared with friends, other pre-owned watch dealers etc)