sequential scans on few columns tables

Hi
Recently I was wondering about tables difficult to index. Example -
queries with "ilike" where clauses. Without additional contrib modules
the only way to search such tables is sequential scan (am I right?)

The point is too keep these tables as small as possible. We can do this
by denormalizing tables. Let's say we have table "users" which we split
into 1:1 relation "users_header" and "users_data". We put searchable
columns into users_header and rest of them into users_data. users_data
have some integer foreign key referencing to users_header.

What do you think about it? Does the Postgres use advantages of small
table users_header? Sequential scan on memory cached table should speed
up queries, the rest columns are in integer-indexed table which
shouldn't slow it down.

These example above is ony an idea, I don't have currently any example
for it.

Regards,
Tomasz Myrta