IMO, you're not going to find 30hp from a "simple" cam swap.
Swap for a streetable roller??? There might be 30hp there.

When the intake and exhaust are both a "cork" limiting airflow through the motor, finding extra power is a challenge. You need to move more air, so you can mix it with more fuel.

If you're really set on retaining the stock appearance, and want a noticable increase in power( and seat of the pants feel), more cubes is your best bet.

When you get tired of that, you can upgrade the intake/exhaust and really bump the power level up.