Setia Emas and Setia Eco Hill is definitely booming semenyih with about 1000 acres of development land. other developments also happening along Jalan Semenyih.
eg. Kiara business centre (entrance of Bandar Sunway Semenyih), pelangi semenyih 2 (by mkh), beside tesco as well (looks like mix development).

personally, i prefer to invest into "up and coming" rather than mature area due to the fact that expensive properties will be the 1st victim if economy crisis attacks.
just my 2 cent