I think you can recharge. Because anyways they will have to upgrade you as per the new plans. So you will be saving around 177 per month if you recharge now (current silver is 849 and new gold is 999). Plus you get one extra month with the semi-annual plan.
But I feel we should wait for the new plans. Because they too might have some long term benefits on semi-annual and annual recharges. Also recharging with the new gold plan gives you
Amazon Prime subscription which you won't get on upgrading from old silver.
PS: Citi bank offer is once per customer. So that is also out of question.