Short answer
Income is relevant to financial planning, but it should not be the only or automatically the most important factor.
Islamic Guidance
What Islam teaches
Islam places importance on responsibility, character and the ability to fulfill rights. Wealth can change, while character and conduct strongly affect the quality of married life.
Practical Guidance
What you can consider
Discuss actual financial responsibilities, existing debts, career plans, living arrangements and expectations. Look for responsible financial behavior rather than only a high current income.
Sources
Qur'an 4:34; Qur'an 65:7.