Question is not should you upgrade to infinnia, it is will they give you one.
So either you have good spend (7.5L in last 6m) on existing card, Or if you have very high nrv or if your rm/bm/ch are competent enough in getting approval.
Imperia doesn't mean anything. If you have salary account and take out all money within 3-4 days, bank earns nothing. Why would bank give high rewards card?
Coming to your second question If you get infinnia invite even paid makes a lot of sense. If your annual spend >7-8L or if you use regular lounge visit.