已知数列\(\{a _{n} \}\)满足\(a_{1}= \dfrac {3}{2}\)，且\(a _{n+1} =λa _{n} +1(n∈N* , λ∈R\)且\(λ\neq - \dfrac {2}{3} ).\)
\((1)λ\)为何值时，数列\(\{a _{n} +1\}\)是等比数列；
\((2)\)若数列\(\{a _{n} +1\}\)是等比数列，求数列\(\{a _{n} \}\)的前\(n\)项和\(S _{n}\)．