(1) Proof: Since $a$ and $b$ are both positive numbers, and $a \neq b$,
we have $$\frac {a}{ \sqrt {b}}+ \sqrt {b} > 2 \sqrt {a}$$ and $$\frac {b}{ \sqrt {a}}+ \sqrt {a} > 2 \sqrt {b}$$,
therefore $$\frac {a}{ \sqrt {b}}+ \frac {b}{ \sqrt {a}} > \sqrt {a}+ \sqrt {b}$$
(2) Solution: According to the problem, $a_1^3 = a_1^2$,
solving this gives $a_1 = 1$ or $a_1 = 0$ (discard),
since $a_1^3+a_2^3 = (a_1+a_2)^2$, i.e., $1+a_2^3 = (1+a_2)^2$,
thus $1+a_2^3 = 1+2a_2+a_2^2$,
solving this gives $a_2 = 2$ or $a_2 = -1$ (discard);
therefore, the values of $a_1$ and $a_2$ are $1$ and $2$, respectively;
since $a_1^3+a_2^3+\ldots+a_n^3 = (a_1+a_2+\ldots+a_n)^2$,
thus $a_1^3+a_2^3+\ldots+a_n^3+a_{n+1}^3 = (a_1+a_2+\ldots+a_n+a_{n+1})^2$.
Subtracting the former from the latter, we get $a_{n+1}^3 = (a_1+a_2+\ldots+a_n+a_{n+1})^2 - (a_1+a_2+\ldots+a_n)^2$,
which simplifies to $a_{n+1}^3 = [2(a_1+a_2+\ldots+a_n)+a_{n+1}]a_{n+1}$,
since $a_n > 0$,
we have $a_{n+1}^2 = 2(a_1+a_2+\ldots+a_n)+a_{n+1}$.
Similarly, $a_n^2 = 2(a_1+a_2+\ldots+a_{n-1})+a_n$ (for $n \geq 2$),
subtracting the latter from the former gives $a_{n+1}^2-a_n^2 = a_{n+1}+a_n$.
Therefore, $a_{n+1}-a_n = 1$.
Since $a_2-a_1 = 1$, it holds that for $n \geq 1$, $a_{n+1}-a_n = 1$,
thus, the sequence $\{a_n\}$ is an arithmetic sequence with the first term as $1$ and common difference as $1$,
hence, the general term formula for the sequence $\{a_n\}$ is $a_n = n$.
So, the conjecture for $a_n$ is $\boxed{a_n = n}$.